GIFT   OF 
MICHAEL  REESE 


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DENTAL 
RADIOLOGY 


BY 


FRANCIS  LE  ROY  SATTERLEE,  Jr.,  A.  M.,  D.  Sc. 

ASSISTANT    TO    THE    PROFESSOR    OF    PHYSICS,     CHEMISTRY    AND     METALI^URGY ; 

LECTURER   ON    physics;    I.ECTURER    ON    RADIOLOGY;    DIRECTOR    OF    PRACTICAL 

PHYSICS     laboratory;     DIRECTOR    OF     X    RAY    LABORATORY;     CHIEF     OF 

X  RAY  SECTION  OF  THE  CLINIC;   NEW  YORK  COLLEGE  OF  DENTISTRY. 


PUBLISHED     BY 

SWENARTON    STATIONERY    COMPANY 

printers    and    publishers 

121   East  27th   Street 

New   York,   N.   Y. 


-^K'^^^^ 


Copyrighted,    1913 
FRANCIS    IvE    ROY    SATTERIvEE^,    Jr. 


TABLE  OF  CONTENTS 

PACK 

INTRODUCTION    7 

CHAPTER  I. 

Early  Investigations  and  Discovery  of  the  X  Ray 13 

CHAPTER  II. 

The    Complete    Spectrum — Invisible    Rays — The    Rays    Com- 
prising the  Study  of  Radiology — General   Properties 19 

CHAPTER  III. 

Ultra     Violet     Rays,     Their     Nature,      Characteristics     and 
Applications    25 

CHAPTER  IV. 

Bi-ultra     Violet     Rays,    Their     Nature,     Characteristics     and 
Applications    29 

CHAPTER  V. 

Tri-ultra    Violet    Rays,    Their    Nature,    Characteristics    and 
How  Generated  in  a  Vacuum  Tube 33 

CHAPTER  VI. 

The   X    Ray   Tube 43 

CHAPTER  VII. 

Symptoms  of  High  and  Low  Vacuum — Remedies  for  Same..     53 

CHAPTER  VIII. 

The    Essentials    of   an    Outfit — Methods    of   Generating    High 
Potential    Electric    Currents — Electrical    Measurements....     59 

CHAPTER  IX. 

Electrical   Induction — Construction   of   X   Ray   Coils 73 

CHAPTER  X. 

The       Interrupter — Tube       Shields — Valve       Tubes — Wiring 
Diagrams     83 

284520 


TABLE  OF  CONTENTS— Continued 

CHAPTER  XL  page 

The  Film  and  Its   Preparation 95 

CHAPTER  XII. 

Application     of     the     Principles     of     Shadows,     to     Avoid 
Distortion    99 

CHAPTER  XIII. 

Technique  of  Taking  the   Picture 107 

CHAPTER  XIV. 

Development   and   Mounting   of    Negatives 119 

CHAPTER  XV. 

Head    Pictures    on    Plates 127 

CHAPTER  XVI. 

Dangers   of  the  X   Ray 131 

CHAPTER  XVII. 

Reading    the    Negatives 177 

CHAPTER  XVIII. 

Diagnosis    of    Pathological    Conditions 181 

CHAPTER  XIX. 

Stereoscopic   Radiographs   of   the   Teeth 191 

CHAPTER  XX. 

Conclusion     195 


PREFACE 

The  author  desires  to  express  his  sincere  thanks  for  sug- 
gestions,  information  or  the  use  of  cuts    from  the   following: 

Mr.  Irwin  Howell,  of  the  General  Electric  Co. 
The  American  X  Ray  Equipment  Co. 
The  Wappler  Electric  Mfg.  Co. 
MacAlaster  &  Wiggin  Co. 
Waite  &  Bartlett  Co. 

Since  this  book  is  written  primarily  as  a  text  book  for  the 
undergraduate  dental  student,  to  be  used  in  the  laboratory,  and 
while  attending  clinical  lectures,  blank  pages  have  been 
inserted  between  the  chapters  to  facilitate  the  student  in  the 
taking  of  additional  notes,  and  to  insure  their  proper  preserva- 
tion associated  with  the  subject  to  which  they  belong. 

It  is  earnestly  hoped  by  the  author  that  all  students  will 
take   advantage   of   these   note   pages    while   attending   lectures. 

Any  suggestions  or  criticisms,  favorable  or  otherwise,  will 
be  welcomed  by  the  author. 


Francis  ht  Roy  Satterlke,  Jr. 

148  East  18th  Street 

New  York  City  August  1,  1913 


INTRODUCTION 

What  Radiology  Means   to  You  —  A 
Plain    Talk    with    the    Undergraduate 

What  real  value  is  Radiology  to  the  dentist?  That  is  a 
question  that  is  being  answered  every  day  by  one's  own  practice, 
although  sometimes  the  practitioner  ignores  or  does  not  under- 
stand the  answer.  Some  of  you  are  willing  to  work  along  in 
the  same  old  rut  and  not  attempt  to  utilize  the  advantages  of  the 
recent  discoveries  in  modern  science,  until  you  become  back 
numbers;  and  then  take  them  up  only  because  you  are  afraid 
to  be  elected  in  the  "fogy"  club  if  you  do  not.  Others  rush 
ahead  heedlessly  into  fields  unknown,  without  blazing  any  trail, 
with  the  result  that  suddenly  they  realize  that  they  are  in  a 
wilderness  and  hopelessly  lost.  Which  is  the  greater  of  these 
two  evils  is  hard  to  say,  but  I  think,  of  the  two,  the  last  man 
has  the  best  chance  to  succeed,  since  some  friend  may  happen 
to  come  along  at  the  moment  he  is  beating  around  looking  for 
the  trail  and  "lead  him  to  it."  But  the  really  successful  man 
is  he  who  goes  through  life  with  his  eyes  open,  his  ears  open, 
and  his  mouth  shut;  his  hands  out  ready  to  grasp  anything  new 
that  comes  along;  to  inspect  it,  study  it,  and,  if  it  appears  to 
be  at  all  useful  to  him,  to  store  it  away  in  his  brain  with  a  tag 
"keep  forward"  on  it;  ever  ready  to  take  it  out  and  refer  or 
add  to  it,  till,  at  length,  he  has  developed  a  subject  full  of 
interest  and  usefulness,  that  has  been  matured  and  ripened  into 
an  established  and  working  rule    or  adjunct  of  his  profession. 

This  is  the  man  who  to-day  will  be  able  to  answer  the 
question  I  first  put  to  you,  and  he  will  tell  you  many  things 


you  litrie.  Hi^aiJied.bL* :  Hfe.'wtiH ^tell  you  first  that  the  subject  of 
Dental  Radiology  embraces  ^quite  a  field,  the  one  part  of  which 
has  been  well  cultivated,  while  the  other  part  is  more  or  less 
barren.  The  cultivated  part  he  will  tell  you  is  that  part  of  the 
subject  which  deals  with  the  X  Ray  as  a  diagnostic  agent;  the 
uncultivated  part  being  the  use  of  the  X  Ray  as  a  therapeutic  ^ 


agent.  .If  he  is  truthful,  he  will  probably  add  that  he  does  not 
mean  to  disparage  the  latter  subject,  but  only  wishes  to  profess 
unfamiliarity  with  it,  although  looking  forward  to  future  de- 
velopments. You  will  probably  ask  this  sensible  man,  if  you 
are  really  seeking  enlightenment,  what  he  has  found  in  the 
X  Ray  to  be  of  any  benefit  to  him  and  how?  He  may  look  at 
you  with  a  supreme  smile  of  pity  and  tell  you  to  open  your 
eyes  and  test  it  yourself,  or  he  may  try  to  explain  some  of 
the  uses  of  the  ray  to  you.  If  he  is  very  generous  and  willing 
to  help  you  along,  and  has,  besides  some  leisure  time,  he  will 
take  you  to  his  ofiice  and  show  you  some  of  the  recent  cases 
that  he  used  the  X  Ray  on,  and  with  what  results.  You  will 
take  out  your  note  book  and  will  make  notes  something  like  this : 
''X  Rays  used  with  good  success  in  cases  of  impacted 
teeth,  non-erupted  and  supernumerary  teeth,  regulating  cases. 
Fractures  of  the  teeth  and  the  maxilla,  inspecting  and  measuring 
curved  roots  and  canals,  pulp  stones,  exostosis,  secondary  den- 
tine, small  pulp  chambers,  length  and  condition  of  root  fillings, 
foreign  bodies  in  the  canals,  old  roots  left  after  extraction, 
faulty  bridge  work,  pericementitis,  alveolar  abscess,  empyema  of 
the  antrum  locating  the  position  of  abnormal  antra,  necrosis, 
absorption  of  alveolus  subsequent  to  old  age  or  extraction  of 
teeth,  chronic  fistulas,  pyorrhea,  showing  the  amount  of  absorp- 
tion in  order  to  determine  whether  the  prognosis  is  good  for 
contemplated  treatment,  epulis,  osteomas,  odontomas  and  tumors 
of  the  oral  cavity  in  general."  When  you  have  finished  putting 
down  this  list  you  will  probably  think  that  there  are  not  many 
conditions  left  to  the  dental  surgeon.  And  you  will  wonder 
whether  all  this  is  true.  Your  friend,  if  he  has  had  much 
experience,  will  turn  to  his  card  index  of  radiographs  and  take 


f 


out  picture  after  picture  with  appended  history,  and  show  you 
cases  of  each  one  of  the  pathological  conditions  he  has  enu- 
merated to  you,  and  your  doubt  will  turn  to  wonder.  On  the 
other  hand,  you  may  not  be  so  lucky  in  finding  as  good  a  friend 
who  will  give  up  his  time  in  explaining  to  you  the  advantages 
of  the  X  Ray,  but  will  let  you  go  your  way  in  blissful  ignorance 
of  the  value  of  so  useful  an  agent. 

While  you  are  in  college  you  will  have  a  short  course  in 
Radiology  that  will  interest  you  for  the  time  being,  but  which 
interest,  in  3.V  probability,  will  be  absorbed  in  the  general  rush 
and  scramble  to  get  through  college  ahead  of  your  fellow  class- 
man with  the  least  possible  study  and  with  the  highest  honors, 
giving  time  only  to  what  you  consider  will  be  your  hard  subjects 
when  you  come  to  the  final  spurt  for  the  much  coveted  D.  D.  S. 
You  will  attain  this ;  subsequently,  you  will  pass  your  State 
Board;  and  eventually  you  will,  with  the  greatest  of  pride  and 
considerable  swelling  of  the  chest  and  head,  hang  out  your 
shingle  in  a  part  of  the  community  where  you  think  you  will 
have  more  chance  than  your  neighbor  to  rapidly  acquire  a 
practice,  and  reap  a  golden  harvest.  Your  ambition  may  per- 
haps be  realized  at  once,  but  alas !  fate  seems  to  have,  in  the 
majority  of  cases,  decreed  otherwise;  and  the  chances  are  that 
you  will  have  often  to  sit  alone  in  your  office  waiting  for  the 
expected  patients,  and  look  out  of  the  window  only  to  see  the 
steady  stream  of  patients  passing  up  the  stoop  of  the  house 
opposite,  where  Dr.  Blank  lives.  You  will  then,  if  you  are  at 
all  human,  feel  the  first  qualms  of  envy  and  you  will  ponder 
why  it  is  Blank  has  such  a  good  practice.  You  will  say  to 
yourself  that  he  is  a  young  man,  too,  and  only  graduated  a 
few  years  ago,  and  you  will  fail  to  understand  what  great 
power  he  has  that  you  do  not  possess.  You  will  then  sit  down 
and  read  the  dental  journals,  and  try  to  improve  your  educa- 
tion and  polish  off  the  rough  work  as  it  came  through  the 
mill  of  your  college  career.  Then  it  is  that  your  thoughts  may 
for  the  first  time  go  back  over  your  years  at  college,  and  you 
will  think  of  your  Radiology  course,  and  remember  the  interest 


it  awakened  in  you  at  that  time.  This  may  even  be  brought 
to  your  mind  by  several  articles  on  X  Ray  in  the  current 
journals.  You  will  wish  your  course  had  been  longer,  and  you 
will  dig  out  your  old  and  now-forgotten  note  books  and  you 
will  find  a  very  few  notes  on  the  subject,  and  you  will  wish,  / 
know  you  will  (many  others  have,  and  they  have  told  me  so), 
that  you  had  only  given  the  subject  more  attention  and  had 
taken  more  notes  when  you  had  the  opportunity.  You  will 
hunt  through  your  journals  and  you  will  probably  discover 
some  very  interesting  article  on  the  subject,  although  somewhat 
out  of  your  depth,  and  behold!  you  may  even  find  one  by  your 
now  much-hated  rival.  Blank,  from  across  the  street. 

All  this  may  happen,  and  again  it  may  not  occur  at  all. 
On  the  other  hand,  you  may  go  years  without  more  than  a 
lingering  occasional  thought  to  the  subject,  but  the  time  will 
come  eventually!  Just  as  surely  as  the  profession  has  advanced 
to  what  it  is,  so  surely  will  the  time  come  when  every  dentist 
will  have  to  admit  Radiology  as  an  integral  and  necessary  part 
of  his  profession.  This  is  no  idle  prophecy  built  on  air  castles, 
or  the  outcome  of  an  enthusiastic  desire  to  see  it  so;  but  I 
assure  you,  these  statements  are  based  on  facts;  and  sta- 
tistics will  bear  me  out  in  showing  the  ever-growing  demand 
for  radiographs  made  on  the  specialist  by  the  dentist;  and  the 
wonderful  increase  in  the  sales  of  the  manufacturers  of  dental 
apparatus  for  X  Ray  work.  It  is  for  this  reason  that  I  am 
urging  one  and  all  of  you  to  give  the  matter  some  thought  and 
go  out  from  your  Alma  Mater  with  some  idea  of  the  value  of 
one  of  the  most  wonderful  and  useful  weapons  nature  has  given 
the  modern  dentist  with  which  to  fight  against  the  difficulties 
and  doubts  that  must  arise  in  your  work.  Not  only  do  I  ask 
you  to  understand  the  subject,  but  I  ask  you  individually  to 
make  one  trial  of  its  value  on  the  first  case  you  have  occasion 
for  it  in  your  practice,  and  to  judge  for  yourself  whether  or 
not  what  I  say  is  true.  You  do  not  have  to  instal  a  complete 
set  of  apparatus  in  your  office  to  do  this;  you  can  send  the 
case  to  a  specialist  who  will,  within  twenty-four  hours,  send  you 

10 


a  finished  radiograph  to  study  and  determine  the  course  of 
treatment.  Do  you  think  it  is  right  to  ignore  the  possibiHty 
of  proving  the  exact  conditions  of  a  doubtful  case?  Is  it  just 
to  yourself  and  your  patient  not  to  take  every  means  within 
your  power  to  ascertain  the  true  condition  of  their  case  before 
you  proceed  to  operate? 

Answer  these  questions  in  the  negative,  and  you  will  per- 
haps discover  why  your  rival  Blank  has  been  so  very  successful. 


11 


NOTES 


12 


CHAPTER  I. 
Early   Investigations   and   Discovery  of  the   X   Ray 

Michael  Faraday  was  the  pioneer  investigator  of  electrical  ^ 
currents  and  vacuum  tubes.  As  early  as  1838  he  conducted  a  - 
series  of  experiments  with  an  electrical  discharge  through  rari- 
fied  gases,  and  invented  the  terms  'anode'  and  'cathode'  for 
positive  and  negative  electrodes.  His  researches  are  now  his- 
torical, inasmuch  as  they  opened  up  a  new  field  of  investigation 
that  was  in  time  to  bear  fruit  in  the  marvelous,  though  acci- 
dental, discovery  of  the  X  Ray. 

Faraday  was  followed  some  time  later  by  Gassiott,  whose 
ideas  were  afterward  carried  out  by  Geissler,  of  Bonn,  the  first 
to  construct  the  tubes  that  now  bear  his  name. 

Up  to  this  time  the  investigations  proved  but  little  of 
importance,  beyond  the  fact  that  any  rarified  gas  gave  off 
a  peculiar  glow,  or  phosphorescence,  when  subjected  to  an 
electrical  discharge  of  high  potential.  This  phenomenon  became 
known  as  'fluorescence!  Air  produced  a  pale  violet  glow, 
hydrogen    a    red,    and    carbon    dioxide    a    steel-blue    shimmer. 

Professor  Hittorf,  the  celebrated  electrical  physicist,  of 
Munster,  next  experimented  with  a  Geissler  tube  of  higher 
degree  of  exhaustion.  He  noticed  an  increasing  resistance  of 
the  electrical  current  to  the  coefficient  of  rarification,  he  also 
found  that  the  color  of  the  gases  under  fluorescence  varied 
with  this  increased  degree  of  rarification  and  that  the  glow 
proceeded  in  straight  lines  from  the  negative  electrode,  casting 
a  shadow  of  an  interposed  object  upon  the  wall  of  the  tube, 
and  he  furthermore  disclosed  the  fact  that  these  rays  were 
capable  of  deflection  by  a  magnet. 

Doctor  Crooks,  afterward  Sir  William,  was  the  next  inves- 
tigator to  enter  the  field  of  research,  and  in  1878  made  some 

13 


interesting  announcements  that  did  a  great  deal  toward  popu- 
larizing the  subject.  He  experimented  with  the  rectilinear 
rays  of  the  Hittorf  tube  and  devised  the  theory  that  the 
rectilinear  path  was  caused  by  the  current  attaching  itself  to 
freely  moving  molecules  of  gas  as  it  left  the  cathode,  and 
proceeded  in  parallel  lines  with  great  velocity,  and  bombarded 
the  opposite  side  of  the  tube,  or  other  intervening  object,  with 
terrific  impact.  Sir  William  Crooks  also  succeeded  in  focusing 
these  rays  of  rapidly  moving  molecules  by  curving  the  cathode, 
thus  giving  to  it  the  form  of  a  concave  mirror,  and  thereby 
projecting  the  rays  to  a  common  point,  instead  of  in  parallel 
lines.  Objects  placed  at  the  focus  of  these  rays  were  heated 
to  whiteness.  This  was  supposed  by  Doctor  Crooks  to  be 
caused  by  the  bombardment  from  the  enormous  quantity  of 
projected  molecules. 

Simultaneously  with  this  announcement  by  Sir  William 
Crooks,  M.  Goldstein  came  forward  with  the  theory  that  the 
phenomenon  was  caused  by  a  transmission  of  energy,  and  not 
by  the  bombardment  with  actual  particles;  but  he  could  not 
give  any  definite  explanation  of  his    'transmitted  energy.' 

Professor  Weidemann,  of  Leipsic,  in  1883,  was  the  first 
to  ascribe  to  the  "Cathode  Rays,"  as  they  began  to  be  called 
because  they  emanated  from  the  cathode  electrode,  the  possi- 
bility that  they  were  in  reality  light  waves  of  extremely  short 
wave-length  at  the  remote  end  of  the  spectrum,  far  beyond  the 
violet  rays.  Paul  Lenard,  a  pupil  of  the  famous  Professor 
Hertz,  also  believed  in  this  hypothesis,  and  in  a  series  of 
experiments  conducted  at  Bonn,  proved  conclusively  that  there 
was  not  only  evidence  of  cathode  rays  outside  of  the  generating 
Hittorf's  or  Crooks'  tube,  but  that,  furthermore,  the  rays  even 
penetrated  a  thin  sheet  of  aluminum  foil,  a  fact  that  none  of 
the  investigators  previous  to  this  had  ever  suspected. 

Prof.  J.  J.  Thompson,  of  the  Cavendish  Laboratory  at 
Cambridge,  by  an  ingenious  method  afterward  succeeded  in 
actually  measuring  the  velocity  of  these  cathode  rays,  which 
he    approximated    to    be    about   200    kilometers,    or    about    124 

14 


miles,  a  second.  It  might  be  well  to  mention  in  reference  to 
Professor  Thompson  that  he  advocated  still  another  theory  in 
regard  to  the  nature  of  the  cathode  rays,  similar  to,  yet  differ- 
ing from  that  of  Crooks,  namely  that  the  molecule  of  electric- 
ally charged  gas,  or  atmosphere,  splits  up  into  two  or  more 
'ions/  This  term,  meaning  'traveler,'  was  so  named  by 
Faraday  who  has  added  largely  to  the  nomenclature  of 
electrical  science, .  a  term  which,  however,  had  long  been  used 
in  connection  with  such  electrically  charged  portions  of  matter 
as  were  known  to  exist  in  the  passage  of  a  current  of  electricity 
through  a  liquid. 

After  a  long  period  of  dormancy  following  the  assertions 
of  Paul  Lenard,  the  world  was  once  more  aroused,  in  the  year 
1895,  by  the  proclamation  of  Prof.  Wilhelm  Conrad  Rontgen, 
that  he  had  discovered  an  entirely  new  ray  differing  from 
any  of  the  cathode  rays  that  had  formerly  existed. 

Like  many  other  great  discoveries,  it  was  brought  about 
through  the  accidental  grouping  of  apparatus  and  conditions 
that  were  just  ripe  to  disclose  to  the  unsuspecting  investigators 
facts  that  had  been  taking  place  time  and  again  unobserved  and 
unrecorded.  In  many  cases  it  has  taken  but  a  simple  incident 
to  disclose  to  the  ever  receptive  and  gifted  minds  of  our  great 
inventors  a  new  truth  that  has  existed  for  untold  years,  and 
needs  but  the  spark  of  intellect  to  develop  and  fan  into  life 
a  new  wonder  that  would  in  time  revolutionize  its  own  field 
of  application. 

So  it  was  that  Professor  Rontgen,  while  experimenting 
with  a  Hittorf  tube  of  high  vacuum  accidentally  stumbled  upon 
a  discovery  so  remarkable  and  unbelievable  at  first,  that 
scientists  and  laymen  alike,  from  every  quarter  of  the  globe, 
paused  in  their  daily  occupations  and  gazed  with  amazement 
and  incredulity  at  the  first  printed  and  brief  reports  of  this 
most  wonderful  discovery.  ''A  new  ray  had  been  discovered 
by  means  of  which  it  was  possible  to  look  through  opaque 
substances !" 

15 


Authenticated  and  more  detailed  reports  were  soon  pro- 
mulgated, and  it  developed  that  another  instance  had  occurred 
where  accidental  grouping  of  conditions  had  born  fruit  little 
suspected  by  the  now  renowned  investigator.  The  conditions 
were  these:  Rontgen  had  covered  his  vacuum  tube  with  black 
cardboard.  He  had  also  coated  another  piece  of  cardboard  with 
the  crystals  of  barium-platino-cyanide,  which  he  was  testing 
for  its  fluorescence  under  cathode  rays.  This  fluorescent 
'screen'  he  had  placed  against  a  table  in  his  laboratory  to  dry 
on  the  opposite  side  of  the  room  from  the  vacuum  tube.  Then 
to  test  the  tube  he  turned  out  the  lights  and  switched  on 
the  current,  passing  the  high  potential  discharge  through  the 
Hittorf  tube  covered  with  black  cardboard.  He  then  suddenly 
became  aware  of  the  fact  that  the  barium-platino-cyanide  screen 
was  glowing  brilliantly  on  the  other  side  of  the  room,  and 
furthermore  in  crossing  the  room  to  examine  it,  he  passed 
between  the  covered  tube  and  the  screen,  and  was  amazed  to 
find  that  a  shadow  was  cast  upon  the  screen !  It  was  only 
this  that  was  needed  to  set  this  experienced  investigator 
directly  upon  the  correct  solution  of  the  apparent  mystery.  He 
at  once  suspected  that  a  new  ray  had  been  found  that  had 
penetrated  the  black  cardboard  covering  of  his  tube  and  affected 
the  screen.  He  now  turned  the  screen  around  with  its  card- 
board back  toward  the  tube.  The  fluorescence  still  continued 
on  the  crystal-coated  side.  The  new  ray  had  also  penetrated 
through  the  back  of  the  screen.  He  next  took  a  large  book  of- 
a  thousand  pages  or  more,  and  held  it  between  the  screen  and 
the  covered  tube;  still  the  glow  persisted.  The  climax  was 
reached  when  on  holding  his  own  hand  between  the  tube  and 
the  screen  he  saw  to  his  utter  amazement  depicted  before  him 
the  complete  shadowgraph  of  his  hand,  and  more  wonderful 
yet,  the  bones  were  outlined  in  solid  black  through  the  less 
dense  flesh  of  the  hand ! 

He    further   discovered   that   these   unknown   rays   had   an 
active  influence  on  a  photographic  plate,  and. that  shadowgraphic 

16 


pictures  of  the  bones  of  the  hand  could  be  obtained  in  this 
manner. 

This  revelation  was  received  by  the  scientific  world  with 
intense  interest,  and  the  enthusiasm  of  the  medical  profession 
was  henceforth  enlisted. 

In  Professor  Rontgen's  original  communication  to  the 
Wurzburg  Physico-Medical  Society,  dated  December  1895,  he 
describes  some  of  his  experiments  and  the  conclusions  that  he 
deduced  from  them.  Among  other  things  he  showed  that  the 
rays  were  not  polarizable,  nor  could  they  be  reflected,  conse- 
quently he  found  that  they  could  not  be  concentrated  by 
lenses.  He  also  discovered  that  the  transparencies  of  different 
bodies  under  these  rays    depended  entirely  upon  their  density. 

He  gave  to  these  wonderful  and  mysterious  rays  the  name 
of  the  algebraic  unknown  quantity  'X,'  and  by  this  name, 
it  is  known  to-day,  notwithstanding  the  subsequent  classi- 
fications of  the  ray  and  the  bestowing  upon  it  of  a  more 
accurate  and  dignified  appellation.  X  Rays  they  were  known 
as,  and  to  the  vast  army  of  experimenters  that  have  taken  up 
their  investigations  X  Rays  they  will  always  remain,  an  excel- 
lent example  of  how  a  popular  misnomer  may  find  its  way  into 
the  nomenclature  of  scientific  literature. 

Professor  Rontgen  concluded  his  original  paper  with  the 
hypothesis  that  these  new  X  Rays  were  perhaps  due  to  longi- 
tudinal vibrations  of  the  ether. 

Since  that  date  there  have  been  a  large  number  of  investi- 
gators in  the  field,  many  of  whom  have  advanced  some 
hypothesis  or  another  concerning  the  exact  nature  of  Rontgen's 
X  Rays,  but  the  old  theory  that  Professor  Weidemann  brought 
forward  in  1883,  in  reference  to  the  cathode  rays,  was  applied 
to  the  Rontgen  radiation  and  is  now  the  only  explanation  that 
has  survived  the  critics  of  the  scientific  world. 

We  will  now  consider  this  present  theory  regarding  the 
nature  of  the  'Rontgen  Rays.' 


17 


THE  COMPLETE  SPECTRUM 


TRl- ULTRA -RED. 
WAVE  LENGTH    -    (VERY  LONG.) 


Bl- ULTRA -RED. 
WAVE  LENGTH      -     18  MICRONS. 


(ELECTRICITY.?) 


Heat 
Rays. 


< 


Optical 
Rays. 


ULTRA- RED. 

WAVE  LENGTH      -       8  MICRONS. 


RED. 
WAVE  LENGTH      -    .71  MICRON. 


ORANGE. 
WAVE  LENGTH      -    .66  MICRON. 


YELLOW. 
WAVE  LENGTH      -    .62  MICRON. 


GREEN. 
WAVE  LENGTH      -     53  MICRON. 


BLUE. 
WAVE  LENGTH     -    .49  MICRON. 


INDIGO. 
WAVE  LENGTH      -    .41  MICRON. 


VIOLET. 
WAVE  LENGTH      -    .38  MICRON. 


ULTRA-VIOLET. 
WAVE  LENGTH      -    .21  MICRON. 


BI- ULTRA -VIOLET. 
WAVE  LENGTH      -    .  1  MICRON. 


TRl -ULTRA -VIOLET. 
WAVE  LENGTH    -    .014  MICRON. 


V 


\   Chemically  ^ 

\         Active 
/  Rays. 


\ 


Finsen 
Rays 


■H-h^^ 


Figure   1 — (see  page  19) 


18 


CHAPTER  11.      ' 

The  Complete  Spectrum — Invisible  Rays — The  Rays  Comprising  the 
Study  of  Radiology — General  Properties 

Figure  1  represents  a  diagram  of  the  complete  spectrum. 
You  have  probably  from  your  physics  associated  the  spectrum 
with  the  seven  primary  colors,  viz. :  violet,  indigo,  blue,  green, 
yellow,  orange  and  red,  but  the  complete  spectrum  shows  the 
presence  of  rays,  both  above  the  red  and  below  the  violet.  The 
three  rays  above  the  red  receive  their  names  from  their  relation 
to  the  nearest  visible  ray,  which  is  red:  the  first  is  called  ultra 
red  (meaning  "beyond  the  red"),  next,  we  have  the  bi-ultra 
red  (meaning  "twice  beyond"),  and  in  the  same  manner  tri- 
ultra  red  indicates  a  group  of  rays  that  is  still  further  removed, 
and  might  therefore  be  considered  as  three  times  beyond  the 
physical  red  ray.* 

Between  the  ultra  red  and  bi-ultra  red  divisions  there  exists 

-  "■       *    '     '* "- — —       T„of  TirViof   trrniin  of  rays  belong  in 

itermine,  although 
:trical  phenomena 
sis  will  never  be 
1   some   degree   of 

entire  phenomena 
ire  invisible  to  the 
leir  effects,  which 
•eak   we   have   the 

ui-wi.xc  x^ . o ^  _  physics  which  we 

know    under  the  general   term   of   'magnetism'    is   included   as 
belonging  to  this  group,  or  division,  of  the  spectrum. 


*  This  nomenclature,  "bi-ultra"  and  "tri-ultra,"  was  suggested  by  the  author  in 
1904  to  take  the  place  of  the  terms  "ultra-ultra"  and  "ultra-ultra-ultra."  See 
Medical  Record  of  January  16,  1904 — "The  Rontgen  or  Tri-ultra  Violet  Rays,  Their 
Nature,   Applications,   and   Dermatological   Effects." 

19 


THE  COMPLETE  SPECTRUM 


Heat 
Ray: 


^< 


TRl- ULTRA -RED. 
WAVE  LENGTH    -    (VERY  LONG.) 


Optical 
Rays 


■'< 


Bl- ULTRA -RED. 
WAVE  LENGTH      -     18  MICRONS. 


(ELECTRICITY.?) 


ULTRA -RED. 

WAVE  LENGTH      -      8  MICRONS. 


RED. 
WAVE  LENGTH      -    .71  MICRON. 


ORANGE. 
WAVE  LENGTH      -    .66  MICRON. 


YELLOW. 
WAVE  LENGTH      -    .62  MICRON. 


GREEN. 
WAVE  LENGTH      -    .53  MICRON. 


V 


ERRATA     Applying  to  figure  1. 

The  FiNSEN  Rays  bracket  should  only  extend  down  to 
and  include  Ultra -Violet  not  Bi- Ultra -Violet  and  Trio- Ultra- 
violet. 

The  Chemically  Active  Rays  bracket  should  only 
extend  up  to  and  include  Red,  not  Ultra- Red. 


^ 


L/-^V- 


Figure   1 — (see  page 


H-t-t--^ 


19) 


18 


CHAPTER  11.      ' 

The  Complete  Spectrum— Invisible  Rays — The  Rays  Comprising  the 
Study  of  Radiology — General  Properties 

Figure  1  represents  a  diagram  of  the  complete  spectrum. 
You  have  probably  from  your  physics  associated  the  spectrum 
with  the  seven  primary  colors,  viz. :  violet,  indigo,  blue,  green, 
yellow,  orange  and  red,  but  the  complete  spectrum  shows  the 
presence  of  rays,  both  above  the  red  and  below  the  violet.  The 
three  rays  above  the  red  receive  their  names  from  their  relation 
to  the  nearest  visible  ray,  which  is  red:  the  first  is  called  ultra 
red  (meaning  "beyond  the  red"),  next,  we  have  the  bi-ultra 
red  (meaning  "twice  beyond"),  and  in  the  same  manner  tri- 
ultra  red  indicates  a  group  of  rays  that  is  still  further  removed, 
and  might  therefore  be  considered  as  three  times  beyond  the 
physical  red  ray.* 

Between  the  ultra  red  and  bi-ultra  red  divisions  there  exists 
a  break  in  the  spectrum.  Just  what  group  of  rays  belong  in 
this  space  we  have  so  far  been  unable  to  determine,  although 
the  theory  has  been  advanced  that  all  electrical  phenomena 
occupy  this  gap.  This  very  likely  hypothesis  will  never  be 
proved  until  we  are  able  to  determine,  with  some  degree  of 
accuracy,  the  wave-length  of  electricity. 

The  ultra  red  rays  are  heat  rays.  The  entire  phenomena 
of  heat  are  grouped  in  this  division.  They  are  invisible  to  the 
eye  and  their  presence  is  known  only  by  their  effects,  which 
are  thermal  in  nature.  Just  above  the  break  we  have  the 
bi-ultra  red  or  magnetic  rays.  That  part  of  physics  which  we 
know  under  the  general  term  of  'magnetism'  is  included  as 
belonging  to  this  group,  or  division,  of  the  spectrum. 


*  This  nomenclature,  "bi-ultra"  and  "tri-ultra,"  was  suggested  by  the  author  in 
1904  to  take  the  place  of  the  terms  "ultra-ultra"  and  "ultra-ultra-ultra."  See 
Medical  Record  of  January  16,  1904 — "The  Rontgen  or  Tri-ultra  Violet  Rays,  Their 
Nature,   Applications,   and  Dermatological   Effects." 

19 


Above  the  bi-ultra  red  comes  the  tri-ultra  red,  or  those 
long  rays  of  the  ether,  called  Hertzian  rays,  now  utilized  in 
wireless  telegraphy. 

In  all  probability  we  have  the  following  sequence:  starting 
with  the  visible  rays  of  red,  which  are  to  a  certain  extent  heat 
rays,  there  is  a  shading  off  gradually  to  the  invisible  rays  of 
heat,  which  are  termed  ultra  red.  Again  we  have  a  shading 
off  from  the  pure  effects  of  heat  to  the  thermo-electrical 
phenomena.  Then  probably  to  the  pure  electrical  phenomena, 
which  are  supposed  to  occupy  the  break  above  the  ultra  red 
rays,  then  to  the  electro-magnetic  phenomena  as  we  approach 
the  bi-ultra  red.  Next  the  phenomena  of  pure  magnetism,  then 
those  long  magnetic  rays  of  the  ether,  and  finally  the  longest 
non-magnetic  Hertzian  or  tri-ultra  red  rays. 

The  only  difference  between  any  of  the  rays  in  the  complete 
spectrum,  from  the  tri-ultra  red  at  the  top  to  the  tri-ultra  violet 
at  the  bottom,  is  the  wave-length.  If  we  had  any  means  of 
changing  the  wave-length  of  one  ray  to  that  of  another,  we 
would  also  change  its  characteristics,  for  example  (the  wave- 
lengths are  given  on  the  diagram  under  their  names),  take 
the  orange  ray  with  the  wave-length  of  .66  of  a  micron  (a 
micron  equals  one  millionth  of  a  meter),  and  suppose  we  had 
some  means  of  shortening  this  wave-length  to,  we  will  say, 
.014  of  a  micron,  we  would  then  change  the  orange  ray  into 
the  tri-ultra  violet.  The  orange  ray  would  lose  its  color,  it 
would  become  invisible  and  it  would  take  on  the  characteristics 
of  the  tri-ultra  violet,  or  in  other  words  it  would  be  converted 
into  the  X  Ray,,  with  all  the  properties  of  the  X  Ray.  With 
the  means  at  present  at  our  disposal  it  is  impossible  to  make 
the  change  in  this  particular  case,  but  there  are  some  instances 
where  we  can  change  certain  rays  into  certain  other  rays,  as 
we  will  see  later  on. 

The  tri-ultra  red,  or  the  Hertzian  rays,  are  the  longest  of 
the  spectrum  rays  and  have  no  approximate  wave-length.  It  is 
the  only  group  of  all  the  rays  in  the  spectrum  that  varies  to 
any  great  extent  in  wave-length,  and  it  is  to  this  fact  that  we 

20 


owe  most  of  the  improvements  in  wireless  telegraphy.  It  makes 
it  possible  for  an  operator  in  one  section  of  the  country  to 
communicate  with  any  given  station  in  any  other  part  of  the 
country,  by  turning  his  system  to  the  same  length  of  wave  as 
that  of  the  one  which  he  wishes  to  call,  thus  securing  selectivity 
in  sending  wireless  messages. 

You  will  note  from  the  diagram  that  the  wave-length 
gradually  decreases  from  the  top  as  you  go  down  toward  the 
bottom  of  the  spectrum.  Starting  with  the  longest  rays  of  the 
tri-ultra  red,  we  come  next  to  the  bi-ultra  red  of  18  microns; 
then  the  ultra  red,  8  microns ;  then  the  red  rays,  .71  of  a 
micron;  the  orange,  .66  of  a  micron;  yellow,  .62,  and  so  on, 
till  we  get  down  to  the  ultra  violet  with  a  wave-length  of  .21 
of  a  micron.  Below  this  we  have  a  still  shorter  ray,  the  bi-ultra 
violet,  with  a  wave-length  of  .1  of  a  micron,  and  finally,  the 
shortest  of  all  known  rays,  the  tri-ultra  violet,  or  the  X  Ray, 
with  a  wave-length  of  .014  of  a  micron. 

The  three  groups  of  rays  that  we  have  to  consider  under 
the  general  heading  of  Radiology,  particularly  in  their  applica- 
tion to  Dentistry,  are  the  ultra,  bi-ultra  and  tri-ultra  violet  rays. 
We  will  consider  first  their  general  properties,  that  is,  proper- 
ties that  are  common  to  them  all,  perhaps  not  to  the  same 
extent  or  to  the  same  degree.  Then  we  will  consider  them 
as  to  their  specific  properties ,  that  is,  the  properties  and 
characteristics  that  each  one  has  in  particular. 

The  first  general  property  to  be  considered  is  the  pene- 
trative power.  They  all  three  have  a  certain  penetrative  power, 
and  the  extent  to  which  each  one  has  this  property  is  governed 
by  a  law  which  we  know  as  the  ''Law  of  Penetration/'  This 
may  be  formulated  as  follows : 

"The  penetration  varies  inversely  with  the  wave- 
length, and  also  with  the  density  and  thickness^  of  the 
substances  to  be  penetrated." 

This  means  that  the  shorter  the  wave-length  the  greater 
the  penetration,  and  conversely,  the  longer  the  wave-length  the 
less   the   penetration.      The   ultra   violet   is   the   longest   of   the 

21 


three  rays,  it  therefore  has  the  least  penetration.  The  tri-ultra 
violet  or  X  Ray  is  the  shortest,  consequently  it  has  the  greatest 
penetration.  Also  the  thicker  and  more  dense  the  substance,  the 
less  readily  will  it  be  penetrated.  Density  and  thickness,  how- 
ever, are  not  the  same  thing.  We  can  have  a  block  of  wood 
measuring  one  cubic  inch;  we  can  also  have  a  block  of  lead  with 
exactly  the  same  volume,  namely,  one  cubic  inch.  One  is  as 
thick  as  the  other,  but  the  lead  is  very  much  denser,  as  is  shown 
by  its  specific  gravity.  The  specific  gravity  is,  therefore,  the 
direct  index  for  the  density,  and  the  greater  the  specific  gravity 
the  denser  the  substance,  and  the  less  readily  will  it  be  pene- 
trated by  these  three  rays. 

Another  general  property  of  the  three  rays  is  their  thera- 
peutic power,  which  varies  to  some  extent  and  with  different 
pathological  conditions.    These  we  will  consider  separately. 

The  third  general  property  is  the  chemically  active  power 
of  the  three  rays.  They  all  have  the  power  of  producing  certain 
chemical  changes  or  reactions  in  certain  substances,  not  to  the 
same  extent,  but  inversely  proportional  to  the  wave-length.  This 
property  is  not  confined  to  these  rays  alone,  but  referring  to 
the  diagram  we  will  see  bracketed  as  the  'chemically  active' 
rays,  the  tri-ultra  violet  to  the  red,  inclusive.  The  red  is  the 
least  chemically  active  and  the  tri-ultra  violet  the  most.  It  is 
for  this  reason  that  we  use  a  red  light  in  the  dark-room  when 
manipulating  photographic  plates  and  films.  The  sensitive 
plate  is  not  affected  by  the  red  light  unless  it  be  exposed  to  it 
for  a  long  time.  Since  the  red  is  so  slightly  chemically  active 
it  does  not  affect  the  sensitive  emulsion  of  the  plate  or  film 
by  producing  chemical  changes  in  the  salts.  The  orange  is 
slightly  more  chemically  active,  and  we  can  use  it  in  the  dark- 
room also,  where  we  have  a  slower  emulsion  of  plates  and  films, 
or  where  we  have  printing  papers  that  are  not  as  sensitive. 
The  yellow  and  the  green  are  a  little  more  actinic  or  chemically 
active,  while  the  blue  is  still  more  so.  The  indigo  and  the 
violet,  and  particularly  the  ultra  violet,  are  also  highly  actinic. 
The  bi-ultra  violet  is  even  more  actinic,  while  the  tri-ultra  violet, 

22 


or  the  X  Ray  is  the  most  actinic  of  all  known  rays.  We  can 
effect  the  sensitive  emulsion  on  a  photographic  plate  after  the 
tri-ultra  violet  has  passed  through  a  block  of  wood  ten  or 
twelve  inches  thick,  or  even  through  a  brick  wall. 

Another  general  property  of  the  rays  which  is  closely 
allied  to  the  chemically  active  power,  is  that  power  which  the 
three  rays  have  of  producing  fluorescence  in  certain  substances. 
It  is  the  phenomenon  that  results  when  we  expose  certain 
substances  to  these  three  rays,  the  substance  giving  off  a  peculiar 
glow  which  resembles  phosphorescence,  and  which  we  call 
fluorescence. 


23 


NOTES 


24 


CHAPTER  III. 

Ultra   Violet   Rays,  Their   Nature,   Characteristics  and   Applications 

We  will  now  consider  each  of  these  three  rays  separately. 
First,  take  the  ultra  violet,  with  a  wave-length  of  .21  of  a 
micron,  the  least  penetrative  of  all  these  three  rays.  A  single 
sheet  of  glass  is  sufficient  to  cut  off  absolutely  all  ultra  violet 
radiation.  The  ray  will  not  penetrate  a  substance  with  a 
density  or  specific  gravity  as  great  as  glass.  We  therefore 
take  'glass'  as  the  limit  of  penetration  for  the  ultra  violet  ray. 
The  ultra  violet  ray  is  produced  in  two  ways :  first,  we  find  it 
in  a  free  state,  in  the  presence  of  an  electrical  spark.  Under 
all  circumstances  and  conditions,  wherever  we  have  an  electrical 
spark,  ultra  violet  rays  are  generated  spontaneously.  It  makes- 
no  difference  where  the  spark  occurs,  whether  it  is  the  spark 
that  we  find  in  an  arc  lamp,  or  whether  it  is  the  spark  occurring 
in  the  spark-coil  of  an  automobile,  or  whether  it  is  the  lightning 
that  we  see  in  the  clouds;  they  are  all  sparks  and  they  all 
produce  tdtra  violet  rays.  It  does  not  matter  whether  the  spark 
takes  place  in  the  air  or  in  a  vacuum,  except  that  in  a  vacuum 
the  spark  is  invisible  and  takes  place  as  a  discharge  or  ionization. 
We  do  not  use  these  ultra  violet  rays  that  are  produced  in 
the  presence  of  a  spark,  except  under  rare  circumstances,  where 
we  produce  the  spark  with  the  intention  of  getting  the  ultra 
violet  ray  from  it.  In  all  other  cases  the  ultra  violet  ray  is 
thrown  out  on  the  atmosphere  as  an  infinite  radiation.  We 
also  find  ultra  violet  rays  directly  in  nature,  in  the  presence 
of  DIRECT  sunlight.  A  single  pane  of  glass  will  cut  off  the 
ultra  violet  rays — we  therefore  have  to  have  the  sun's  rays  in  the 
open  and  not  coming  through  a  glass  window.  It  is  supposed 
by  some  scientists  that  even  these  ultra  violet  rays  come 
originally   from  an   electrical   spark,  this  spark  taking  place   in 

25 


the  atmosphere  of  the  sun,  as  an  ionization  of  the  gases  that 
envelop  that  planet.  Of  course  this  is  only  a  theory  and  lacks 
the  necessary  proof,  although  the  supposition  seems  plausible. 
The  therapeutic  effects  of  the  ultra  violet  rays  are  very 
marked  in  tubercular  conditions  of  the  skin.  The  disease  which 
is  known  as  'lupus  vulgaris'  yields  most  readily  to  ultra  violet 
radiation.  Doctor  Finsen,  of  Copenhagen,  Denmark,  was  one 
of  the  first  to  utilize  this  property  of  the  ultra  violet  rays,  and 
he  did  so  in  an  especially  constructed  lamp.  His  apparatus 
consists  first  of  a  series  or  'bank'  of  arc  lights,  the  electrodes 
of  which,  instead  of  being  constructed  of  carbon,  as  most  arc 
lamps  are  that  we  use  for  illumination,  are  made  of  iron  or 
copper,  as  he  found  that  these  two  metals  when  used  as 
electrodes  gave  off  much  richer  radiations  of  ultra  violet  rays. 
These  rays  he  collected  by  means  of  a  parabolic  mirror  and 
concentrated  them  through  a  large  telescope,  the  inverted  end, 
or  objective,  of  which  was  presented  to  the  arc  lamps.  The 
lenses  of  this  telescope  were  of  peculiar  construction;  they 
could  not  be  made  of  glass,  as  the  ultra  violet  ray  would  not 
traverse  them.  He  had  to  construct  them  of  a  substance  that 
had  a  lesser  specific  gravity  than  glass,  so  he  used  quartz  and 
colored  it  cobalt  blue,  which  absorbed  all  the  other  light  and 
heat  rays  of  the  spectrum,  and  allowed  only  the  blue,  indigo, 
violet  and  ultra  violet  rays  to  pass.  You  will  see  in  Figure  1 
these  four  rays  bracketed  and  classified  as  'Finsen  Rays.'  The 
small  end  of  the  telescope  was  focused  upon  a  patient  who 
reclined  on  a  couch  below  the  apparatus,  and  these  powerful 
rays,  particularly  those  of  the  ultra  violet,  when  allowed  to 
radiate  over  a  surface  of  lupus,  caused  a  destruction  of  the 
tubercle  bacilli  and  cured  the  lesion.  The  percentage  of  cures 
has  been  estimated  to  be  as  high  as  97%  of  cases  when  treated 
with  Finsen  rays,  and  the  only  reason  that  it  is  not  100%  is 
that  we  have  to  allow  about  3%  of  failures  due  to  faulty 
technique  on  the  part  of  the  operators,  and  also  of  the  inability 
of  patients  to  continue  the  prescribed  treatments. 

26 


There  are  a  number  of  other  skin  diseases  for  which  the 
ultra  violet  ray  also  possesses  a  therapeutic  value,  but  perhaps 
not  to  as  great  an  extent  as  those  shorter  rays  which  we  will 
now  consider  as  the  bi-ultra  violet. 


27 


NOTES 


28 


CHAPTER  IV. 
Bi-ultra  Violet  Rays,  Their  Nature,  Characteristics  and  Applications 

The  bi-ultra  violet  ray  has  a  wave-length  of  .1  of  a  micron. 
It  has  a  greater  penetrative  power  than  the  ultra  violet;  it 
will  pass  quite  readily  through  thin  sheets  of  aluminum,  one  of 
the  lightest  of  the  metals,  but  will  not  pass  through  heavier 
metals.  Aluminum  is,  therefore,  the  limit  of  penetration  of 
these  rays. 

Bi-ultra  violet  rays  are  obtained  in  two  ways: — First, 
by  the  breaking  up  of  the  ultra  violet  into  still  shorter  rays 
in  the  presence  of  a  vacuum  tube;  and  directly,  in  nature, 
in  the  presence  of  all  radio  active  substances,  such  as  radium, 
actinium,  polonium,  uranium  and  many  others.  These  rays 
differ  but  very  slightly  from  the  ones  generated  in  the  vacuum 
tube,  their  characteristics  are  almost  identical,  and  it  is  only  in 
the  wave-length  which  is  slightly  shorter  that  we  note  any 
distinction  whatsoever.  Bi-ultra  violet  rays  are  used  quite  a 
little  in  the  treatment  of  superficial  cases  of  cancer.  They  are 
also  used  to  a  very  great  extent  when  combined  with  currents 
of  high  frequency  and  high  potential  in  the  modern  treatment 
of  rheumatism;  very  good  results  can  be  obtained  by  this 
method.  Cases  of  ankylosed  and  stiffened  joints  can  be  broken 
up  and  deposits  of  uric  acid  dissolved,  but  the  best  results  are 
only  obtained  when  a  correct  technique  is  used  in  the  adminis- 
tration of  the  treatment,  together  with  proper  diet  and  alkaline 
medication. 

In  dentistry  we  utilize  the  bi-ultra  violet  ray  in  the  treat- 
ment of  pyorrhea  alveolaris,  by  means  of  the  author's  vacuum 
electrodes,  especially  designed  for  the  purpose,  with  excellent 
results  when  the  technique  is  carefully  and  faithfully  carried 
out. 

29 


The  therapeutic  value  of  the  rays  given  off  by  radium  is 
so  closely  identified  with  the  vacuum  tube  rays  that  the  results 
have  proven  to  be  about  the  same.  You  will  remember  when 
radium  was  first  discovered  by  those  two  great  French  chemists, 
Monsieur  and  Madame  Curie,  how  all  the  newspapers  and  the 
medical  and  scientific  journals  took  up  and  exploited  the  won- 
derful new  element,  'Radium.'  To-day  we  do  not  see  quite  so 
much  about  radium  in  the  scientific  journals  and  practically 
nothing  in  the  newspapers.  Does  that  mean  that  radium  has 
lost  its  power,  or  to  what  do  we  attribute  this  falling  off  in 
the  use  of  radium?  The  reason  is  this:  It  was  found  exceed- 
ingly difficult  to  extract  the  pure  bromides  of  radium  from  the 
ore,  the  process  requiring  a  long  time  and  a  great  amount  of 
work  which,  therefore,  made  the  cost  of  pure  radium  enor- 
mously high.  We  have  not  one  pound  of  pure  metallic  radium 
in  the  world  to-day,  and  if  we  had,  it  is  estimated  that  it 
would  cost  just  about  $33,000,000.  With  a  small  vacuum 
electrode  that  can  be  purchased  for  about  $1.50  we  can  generate 
bi-ultra  violet  rays  of  equal  power  and  volume  to  those  emanat- 
ing from  ten  pounds  of  radium.     That  is  the  explanation ! 

There  are  certain  cases,  however,  where  the  rays  given  off 
by  radium  can  be  used  where  we  cannot  use  the  vacuum  rays, 
principally  in  the  treatment  of  cavity  conditions.  For  example, 
in  the  treatment  of  a  case  of  cancer  of  the  stomach,  we  take  a 
small  vial  of  radium,  place  it  in  a  stomach  tube  and  lower  it 
directly  into  the  stomach  in  close  proximity  to  the  diseased 
lesion.  This  you  cannot  do  with  a  vacuum  electrode.  Radium 
has  no  application  to  dentistry  to-day,  although  at  one  time 
its  use  was  advocated  by  two  Holland  dentists  who  thought  that 
its  analgesic  powers  could  be  utilized  in  the  treatment  of 
pulpitis  by  the  placing  of  a  tiny  vial  in  the  root  canal  of  an 
aching  tooth.  The  dental  profession,  however,  did  not  take  up 
the  idea  and  preferred  the  inexpensive  use  of  arsenic  or 
'pressure-anesthesia'  and  the  removal  of  the  offending  pulp  and 
filling  the  canal. 


30 


NOTES 


31 


NOTES 


32 


CHAPTER  V. 

Tri-ultra    Violet    Rays,    Their    Nature,    Characteristics,    and    How 

Generated  in  a  Vacuum  Tube 

The  wave-length  of  the  tri-ultra  violet  ray  is  .014  of  a 
micron.  It  is  situated  at  the  very  lower  end  of  the  spectrum 
and,  being  the  shortest  wave  length  of  the  three  rays,  it  has, 
therefore,  according  to  the  law  of  penetration,  the  greatest 
penetrative  power.  It  will  penetrate  all  substances — even  gold, 
platinum  and  silver — the  densest  metals,  in  thin  sheets.  The 
therapeutic  properties  of  the  tri-ultra  violet  or  the  X  Ray  are 
very  marked;  one  of  its  principal  effects  being  its  analgesic 
power.  We  frequently  find  that  in  the  short  exposure  necessary 
for  the  taking  of  a  radiograph  the  pain  from  an  acute  attack 
of  neuralgia  of  the  fifth  nerve,  or  from  an  ulcerated  tooth  is 
quite  relieved,  and  its  effects  sometime  seem  almost  magical. 
Nevertheless,  it  is  a  most  dangerous  method  to  use  for  the 
relief  of  pain,  and  should  never  he  resorted  to,  particularly  by 
the  dentist,  as  there  is  always  the  temptation  to  repeat  the 
dose  too  often  at  the  urgent  request  of  the  patient,  and  conse- 
quently to  produce  conditions  that  are  very  hard  to  heal.  How- 
ever, these  conditions  we  will  take  up  in  a  subsequent  chapter. 

The  X  Ray  is  used  in  many  cases  of  cancer  with  very  good 
results,  and  where  the  cancer  is  superficial  we  have  very  often 
been  able  to  attain  a  cure.  If  the  cases  are  those  of  deep- 
seated  tumors  it  is  more  difficult  to  get  good  results,  inasmuch 
as  we  have  to  penetrate  healthy  tissue  to  get  at  the  cancerous 
lesion.  Cancers  of  the  skin,  therefore,  can  be  said  to  yield 
very  readily  to  X  Ray  treatment.  Those  situated  near  the 
surface,  as  for  instance,  cancers  of  the  breast,  are  more  diffi- 
cult, but  very  good  results  have  been  obtained,  particularly 
if  we  can  operate  first.     The  modern  technique  in  the  treatment 

33 


of  cancer  is  to  operate  first,  wherever  possible,  and  immediately 
after  an  operation  to  follow  up  with  a  series  of  X  Ray  treat- 
ments, even  through  the  dressings.  This,  in  most  cases,  prevents 
recurrence.  There  are  many  skin  diseases  that  yield  more  or 
less  to  X  Ray  radiation,  among  which  many  be  mentioned  lupus 
vulgaris;  lupus  erythematosus;  carcinoma,  external,  scirrhus 
and  epithelioma;  sarcoma;  enlarged  glands,  scrofulous  or  other- 
wise; goitre,  simple  and  exophthalmic;  sycosis  and  favus;  mol- 
luscum  contagiosum;  phthisis,  pulmonary  and  laryngeal;  rodent 
ulcer;  hypertrichosis;  pruritus;   eczema;  acne;  warts,  etc.,   etc. 

Let  us  now  see  how  we  can  obtain  these  three  rays.  We 
will  refer  to  Figure  2,  which  represents  the  interior  of  a  large 
X  Ray  tube. 

We  will  suppose  that  we  have  a  sphere  of  glass  from  which 
most  of  the  air  is  exhausted,  consequently  there  exists  a  state 
of  partial  vacuum.  Vacuums  are  referred  to  as  "high," 
''medium"  and  "low,"  a  complete  vacuum  being  impossible  to 
attain.  A  high  vacuum  is  where  only  one  millionth  part  of  the 
original  air  remains;  or  an  equivalent  pressure  of  about  .0003 
millimeters  of  mercury,  while  a  medium  vacuum  would  have  one 
hundred  thousandth  part  of  the  original  air,  and  a  low  vacuum 
would  be  where  one  thousandth  part  remains,  or  an  equivalent 
pressure  of  about  .005  millimeters  of  mercury. 

In  this  sphere  of  glass  (A)  or  X  Ray  tube,  as  we  will 
call  it,  we  have  the  condition  of  medium  vacuum,  i.  e.,  a 
hundred  thousandth  per  cent,  vacuum,  which  is  about  the 
degree  of  exhaustion  necessary  for  satisfactory  dental  work. 
In  this  tube  we  have  two  metal  electrodes  represented  in  the 
diagram  by  the  lines  DWE  and  FXG.  They  are  disks  of  metal 
placed  at  opposite  sides  of  this  tube  and  parallel  with  each 
other.  They  are  connected  by  wires  passing  through  the  glass 
wall  to  terminals  on  the  outside,  C  and  B,  which  can  in  turn 
be  connected  with  the  source  of  electricity.  We  will  now  pass 
a  high  potential  current  of  electricity  through  this  tube,  i.  e.,  a 
current  of  from  60,000  to  180,000  volts.  This  high  potential 
current,  the  nature  of  which  we  will  take  up  a  little  later,  enters 

34 


Figure  2 — (see  page  34) 


35 


at  the  cathode  or  the  negative  side,  marked  in  the  diagram  by 
the  minus  sign,  passes  through  the  tube  across  the  vacuum 
gap  and  impinges  upon  the  anode  or  positive  electrode  marked 
by  the  positive  or  plus  sign.  The  velocity  of  the  electric 
current  through  a  low  vacuum  has  been  estimated  to  be  about 
124  miles  per  second.  The  current  leaves  the  cathode  disk 
(DWE)  in  the  form  of  an  invisible  spark  or  electrical  dis- 
charge. As  we  have  said,  wherever  an  electrical  spark  takes 
place  ultra  violet  rays  are  produced;  therefore,  ultra  violet  rays 
are  spontaneously  produced  all  over  the  surface  of  this  cathode 
disk.  These  rays  take  the  path  of  the  current;  they  travel 
through  the  tube  with  the  same  velocity  (about  128  miles  per 
second  in  a  medium  vacuum),  in  parallel  lines,  as  indicated 
by  the  dotted  lines  in  the  diagram,  until  they  strike  upon  the 
anode  FXG,  at  the  positive  side  of  the  tube. 

The  enormous  velocity  under  which  these  rays  travel  causes 
a  shortening  of  the  wave  length.  This  may  be  illustrated  by  a 
simple  simile.  Take  a  long  coil  of  rope  and  fasten  one  end 
to  a  post,  and  stand  off  some  distance  with  the  other  end  of 
the  rope  in  your  hand ;  very  slowly  shake  the  end  up  and  down, 
and  you  will  start  a  series  of  large  waves,  or  a  wave  motion,  in 
this  rope.  If  you  increase  the  velocity  with  which  you  shake 
this  rope  up  and  down,  your  waves  will  become  shorter.  This 
is  analogous  to  what  takes  place  in  the  vacuum  tube.  The  great 
velocity  under  which  these  rays  travel  causes  the  wave-length 
of  .21  of  a  micron  to  be  reduced  to  about  .1  of  a  micron.  The 
ultra  violet  rays,  therefore,  lose  their  individuality  and  take  on 
the  characteristics  of  the  bi-ultra  violet  ray,  which  has  a  wave- 
length of  about  .1  of  a  micron.  Just  where  this  transformation 
takes  place  we  do  not  know.  It  may  be  close  to  the  cathode  or 
it  may  be  close  to  the  anode,  or  it  may  be  just  half  way 
between;  it  makes  no  difference  as  to  the  ultimate  result.  The 
bi-ultra  violet  rays,  when  once  formed  by  the  breaking  up  of  the 
ultra  violet  into  the  shorter  wave-length,  continue  until  they  at 
last  strike  upon  the  metallic  surface  of  the  anode.  Here  they 
undergo  their  second  transformation.     The  original  ultra  violet 

36 


rays  had  been  reduced  in  wave-length  to  as  great  an  extent  as 
possible,  by  the  velocity  alone  under  which  they  were  traveling. 
Now  add  to  that  velocity  the  sudden  force  of  impact  against 
the  solid  anode  and  we  get  a  still  greater  reduction  in  the 
wave-length.  The  bi-ultra  violet  rays  are  shattered.  The  wave- 
length decreases  from  .1  of  a  micron  to  about  .014  of  a  micron; 
or,  in  other  words,  the  bi-ultra  violet  ray  is  transformed  into 
tri-ultra  violet,  or  the  X  Ray.  The  greater  the  velocity  with 
which  these  rays  travel  the  greater  will  be  the  impact  against 
the  anode,  and  the  shorter  will  be  the  wave-length  resulting 
from  the  impact. 

If  the  tube  was  actually  constructed  with  the  electrodes 
as  represented  by  the  lines  DWE  and  FXG,  in  Figure  2,  we 
would  not,  in  all  probability,  get  the  double  shortening  of  the 
wave-length.  The  bi-ultra  violet  rays  would  not  be  reduced  to 
a  wave-length  as  .014  of  a  micron,  because,  when  they  strike 
upon  the  anode,  they  would  be  reflected  directly  back  upon  the 
approaching  rays,  and  would  tend  to  retard  these  rays,  conse- 
quently their  force  of  impact  would  be  considerably  reduced. 
The  reflected  ray  would  not  have  as  short  a  wave-length  as  it 
would  if  the  approaching  rays  were  not  retarded. 

To  remedy  this  eflfect  we  change  the  position  of  the  anode 
and  swing  it  to  an  angle  of  45  degrees  with  the  vertical.  The 
line  FXG  now  becomes  the  line  HXK.  As  the  rays  strike 
upon  this  surface  they  are  reflected  downward,  and  consequently 
will  not  tend  to  retard  the  approaching  rays.  Still  it  would 
be  nearly  impossible  to  obtain  an  X  Ray  picture  from  such  a 
tube.  The  reason  for  this  is  that  the  rays  emanate  from  a 
series  of  points  upon  the  anode,  instead  of  one  single  point. 
If  the  area  of  the  surface  of  the  cathode  disk  were  one  square 
inch  we  could  readily  conceive  of  one  million  points  of  electrical 
discharge  from  this  disk.  Each  point  of  discharge  would 
generate  its  own  ultra  violet  ray.  We  would  then  have 
one  million  parallel  'beams'  of  ultra  violet  ray  traversing  the 
tube,  and  they  would  consequently  strike  upon  the  anode  in 
one  million  points.     From  each  point  X  Rays  would  be  gener- 

37 


ated  and  we  would  therefore  have  X  Rays  emanating  from  one 
million  points.  You  will  readily  see  that  a  tube  of  that  kind 
would  be  useless  to  take  a  radiograph  with,  since  an  X  Ray  pic- 
ture is  essentially  a  shadowgraph,  and  in  this  case  there  would 
be  no  sharp  or  distinct  shadows.  If  you  were  to  stand  ten  can- 
dles in  a  row  in  front  of  a  screen,  and  then  place  your  hand 
between  the  ten  candles  and  the  screen,  there  would  be  ten 
shadows  of  your  hand  thrown  upon  the  screen,  none  of  which 
would  be  very  sharp.  They  would  all  be  blurred  and  hazy;  but 
if  we  were  to  merge  all  these  ten  candles  into  one  candle  of 
ten  candlepower,  we  would  have  as  a  resulting  shadow  only 
one  outline  of  the  hand  with  ten  times  the  intensity  of  shadow, 
but  sharp  and  well  defined.  To  accomplish  this  result  in  the  X  Ray 
tube  we  must  bring  these  beams  of  approaching  bi-ultra  violet 
rays  to  a.  point,  and  that  point  must  be  upon  the  surface  of  the 
anode.  We  must  therefore  change  the  shape  of  the  cathode 
disk.  Instead  of  a  straight  disk,  as  shown  in  Figure  2,  by  the 
line  DWE,  we  give  to  it  the  form  of  a  concave  mirror  shown 
by  the  line  DNE,  and  we  place  it  at  such  a  distance  from 
the  anode  as  to  bring  its  principal  focus  directly  to  a  point  upon 
its  surface. 

This  is  one  of  the  most  essential  principles  in  the  con- 
struction of  an  X  Ray  tube.  The  tendency  on  the  part  of 
many  manufacturers  is  to  get  an  imperfect  or  'coarse  focus,' 
with  the  result  that  X  Rays  emanate  from  a  series  of  points, 
instead  of  from  one  single  point.  Pictures  made  with  tubes  of 
this  character  are  not  as  clear  as  they  would  be  if  the  tube  had 
a  'pin-point'  focus.  In  purchasing  a  tube,  when  the  manufac- 
turer 'tries  it  out'  for  you,  as  he  generally  will,  you  should 
notice  whether  the  point  of  light  upon  the  surface  of  the  anode 
is  a  'pin  point'  or  whether  it  is  one-eighth  or  even  one-quarter 
of  an  inch  in  diameter,  as  we  sometimes  find,  and  reject  tubes 
where  the  focus  is  not  sharp. 


38 


NOTES 


39 


NOTES 


40 


NOTES 


41 


SECTIONAL    DIAGRAM    OF    X    RAY    TUBE 


Figure    3 — (see    page    43) 


42 


CHAPTER  VI. 
The  X  Ray  Tube 

Figure  3  represents  a  sectional  diagram  of  a  modern  X  Ray 
tube.  We  note  that  the  sphere  of  glass  has  two  elongations  at 
either  end  through  which  the  electrodes  FB  and  EA  pass. 
These  elongations  separate  the  external  connections  for  the  high 
potential  current,  making  a  greater  air  gap  for  the  current  to 
jump  than  if  the  external  connectors  were  on  wall  of  the 
sphere  itself  as  in  Figure  2.  This  arrangement  forces  the 
current  to  pass  through  the  resistance  of  the  vacuum  rather 
than  overcome  the  greater  air  resistance  from  A  to  B  on  the 
outside  of  the  tube.  A  plane,  KL,  passing  through  the 
tube  and  coinciding  with  the  surface  of  the  anode,  divides  the 
tube  approximately  into  two  hemispheres;  the  lower  hemisphere 
ONP  is  called  the  hemisphere  of  activity,  and  the  upper  one, 
VMW,  the  hemisphere  of  non-activity.  Anything  placed  on  the 
lower  side  of  the  plane,  KL,  would  be  subjected  to  the 
radiation  of  the  X  Rays,  anything  placed  on  the  other  side  of 
the  plane,  KL,  would  receive  no  rays  whatever. 

We  note  in  looking  at  this  diagram.  Figure  3,  the  third 
electrode,  CG,  which  is  marked  with  the  positive  sign.  We 
therefore  infer  that  it  must  be  an  anode,  and  we  note  also  that 
it  is  connected  exteriorly  by  means  of  a  wire  to  the  main  anode. 
The  shape  of  the  inside  surface,  G,  is  usually  a  flat  disk.  The 
purpose  of  this  electrode  is  to  act  as  a  safety  valve  for  the  elec- 
trical current.  It  answers  the  same  purpose  to  the  tube  as  the 
safety  valve  does  on  the  steam  boiler  of  an  engine.  If  we  throw 
in  too  great  a  pressure  of  steam,  the  safety  valve  blows  open 
and  the  surplus  steam  escapes,  thereby  preventing  an  explosion 
of  the  boiler.  The  same  thing  takes  place  in  the  tube.  If  we 
throw   in  too  heavy  an   electrical   discharge,   so   great  that  the 

43 


capacity  of  the  main  anode  cannot  carry  it  off,  the  secondary 
anode  takes  up  this  surplus  electricity  and  conveys  it  out  of 
the  tube  and  joins  it  to  the  conducting  wire,  returning  it  to  its 
circuit,  consequently  preventing  the  current  from  striking  the 
glass  wall  of  the  tube  and  puncturing  it. 

All  tubes  are  not  constructed  with  this  secondary  anode. 
If  the  capacity  of  the  main  anode  is  large  enough  to  carry  off 
the  heaviest  current  that  we  can  force  through  the  tube,  there 
is  no  need  for  this  extra  electrode  which  is  known  by  several 
names.  It  has  been  called  a  secondary  anode,  an  auxiliary 
anode,  and  an  anti-cathode,  but  the  term  principally  used  is 
the  bi-anode. 

The  main  anode  of  the  tube  is  constructed  of  three  metals : 
first  a  disk,  which  is  generally  made  of  an  alloy  of  platinum 
and  iridium,  or  even  a  tungsten  button,  to  withstand  the  very 
intense  heat  of  the  electrical  discharge,  focused  to  a  single 
point,  together  with  the  bombardment  of  the  bi-ultra  violet  rays 
upon  its  surface.  This  heat  is  so  intense  that  if  we  had  but 
the  disk  of  platinum  alone  it  would  be  immediately  melted. 
It  is  therefore  necessary  to  construct  it  of  platinum  alloy  of 
the  highest  fusing  point,  or  else  with  a  tungsten  button  set 
into  a  surface  of  copper  or  brass.  We  next  back  up  this  disk 
of  alloy  with  a  solid  block,  F,  of  copper  or  brass,  the  block 
in  turn  being  mounted  on  a  hollow  iron  core  extending  back 
into  the  narrow  neck  of  the  tube.  The  purpose  of  this  iron 
core  and  solid  block,  back  of  the  disk  or  'target/  as  it  is  very 
often  called,  is  to  conduct  the  heat  away  from  the  surface,  and 
distribute  it,  thereby  reducing  the  intensity  upon  the  surface 
of  the  target.  Figure  4  represents  an  illustration  of  the  modern 
type  of  X  Ray  tube,  made  by  the  Macalaster,  Wiggin  Co.,  of 
Boston,  Mass. 

Another  thing  you  will  observe  while  the  current  is  passing 
through  the  vacuum  is  the  green  coloration  in  the  tube.  This 
green  color  is  not,  as  many  people  suppose,  the  X  Ray  itself 
(which  you  will  remember  is  invisible),  but  is  due  to  the 
fluorescence   of   the   rarified   gas   remaining   in   the   tube   after 

45 


partial  exhaustion.  The  coloration  depends  on  two  things: 
first,  on  the  kind  of  gas,  and  second,  the  quantity  of  gas 
present. 

In  the  X  Ray  tube  we  have  to  deal  only  with  one  kind  of 
gas,  and  that  is  the  atmospheric  air  which  it  originally  con- 
tained. Upon  exhaustion  we  leave  it  in  a  rarified  state,  and 
therefore,  in  passing  a  current  of  high  potential  electricity 
through  it,  it  gives  off  this  peculiar  glow  or  fluorescence.  This 
fluorescence,  or  coloration  of  the  gas  in  the  tube,  serves  us  as  a 
guide  or  index  to  the  degree  of  vacuum,  or  exhaustion,  of  the 
tube;  in  fact,  we  have  no  other  means  of  determining  the 
quantity  of  gas  in  the  tube.  Unfortunately  there  is  no  meter 
or  gage  that  we  can  attach  to  the  tube  and  take  a  direct  reading 
of  its  state  of  vacuum.  We  have  to  rely  on  our  experience 
in  the  judging  of  the  coloration,  assisted  by  the  reading  of 
the  milliamperes  passing,  as  to  whether  the  tube  has  a  proper 
degree  of  vacuum  or  not.  'We  will  consider  the  coloration  of 
air  at  different  degrees  of  rarifaction.  We  will  start  at  very 
low  vacuum  and  go  up  to  very  high.  A  tube  of  very  low 
vacuum  is  red,  and  as  the  vacuum  increases  the  red  changes 
to  violet,  the  violet  to  blue,  the  blue  to  green,  then  through  all 
the  varied  delicate  shades  of  green,  from  very  dark  to  very 
light,  until  at  last  we  come  to  a  bright  canary  yellow  of  highest 
vacuum.  The  entire  range  of  efficient  work  in  an  X  Ray  tube 
used  for  dental  work  may  be  classified  under  the  different 
shades  of  green,  from  dark  to  light  olive.  Experience  only 
will  determine  the  correct  shade  of  green  for  the  taking  of  a 
proper  picture  of  the  part  in  question.  The  degree  of  vacuum 
of  a  tube  means  a  great  deal  to  the  operator,  because  it  governs 
the  amount  of  penetration  of  the  X  Rays;  the  higher  the 
degree  of  vacuum  the  more  penetrating  will  the  rays  be,  and 
the  velocity  with  which  the  rays  and  electrical  current  traverse 
the  vacuum  will  be  greater.  The  rays  are  therefore  broken  into 
shorter  wave-lengths,  and  under  the  law  of  penetration  the 
shorter  the  wave-length  the  greater  the  penetration;  the  con- 
verse is  true  in  low  vacuum.     In  low  vacuum  tubes  we  have 

46 


a  greater  volume  of  rays,  and  therefore  a  better  or  more 
brilliant  coloration  than  in  the  higher  degrees  of  vacuum, 
because  the  resistance  of  the  vacuum  is  not  as  great  to  the 
electrical  current,  and  consequently  more  current  passes  through 
the  tube  and  more  rays  are  generated,  but  they  lack  the 
intensity  because  they  do  not  travel  with  a  speed  sufficiently 
rapid  to  cause  a  breaking  up  into  the  shortest  wave-lengths. 
In  the  higher  vacuum  tubes,  as  the  resistance  increases  to 
the  electrical  discharge,  some  of  the  current,  instead  of  passing 
through  the  tube,  jumps  around  the  outside  as  a  static  discharge. 
In  that  case  we  only  utilize  part  of  the  current,  and  therefore 
have  a  reduced  volume  of  rays,  but  those  rays  travel  with  a 
greater  velocity  and  generate  more  penetrating  X  Rays.  A 
strange  thing  about  all  X  Ray  tubes  is  that,  in  an  absolutely 
closed  and  hermetically  sealed  tube,  the  quantity  of  gas  varies. 
This  apparently  paradoxical  phenomenon  can  be  explained  by 
the  fact  that  all  substances  are  porous ;  porosity  being  one  of 
the  general  properties  of  matter,  and  in  the  pores,  or  between 
the  interstices  of  all  matter,  we  have  in  most  cases  air.  So  in 
the  metal  parts,  and  even  in  the  glass  itself,  of  this  tube,  we 
have  particles  or  molecules  of  air  that  have  been  held  between 
the  pores  or  interstices.  Another  principle  of  physics  is  that 
when  bodies  are  heated  they  expand,  and  in  the  expansion 
they  drive  off  the  confined  air.  When  we  pass  a  current  of 
electricity  through  the  tube  one  of  the  first  phenomena  that 
occurs  is  the  generating  of  heat  in  the  metallic  parts  of  the 
tube  by  resistance  to  the  electrical  current.  Electrical  energy  is 
transformed  into  heat  energy.  The  heat  thus  transformed 
causes  the  metals  and  the  glass  itself  to  expand.  The  air  that  was 
confined  in  them  is  therefore  driven  off  and  added  to  the  supply 
already  present  in  the  tube,  and  consequently  lowers  the  degree 
of  vacuum.  When  the  tube  is  allowed  to  cool  again  the  gases 
are  once  more  absorbed  by  the  metals  and  by  the  glass  that 
gave  them  off,  but  strange  to  say,  a  little  more  gas  is  absorbed 
than  was  originally  given  out.  Just  what  causes  this  is  not 
known,  but   the   fact   remains,   and  consequently    we   find   that 

47 


the  more  we  use  a  tube  the  higher  vacuum  it  will  become.  Each 
time  we  pass  an  electrical  current  through  the  tube  we  will 
probably  note  that  it  is  a  little  bit  higher  in  vacuum  than  it 
was  the  time  before. 

Since  the  vacuum  has  a  tendency  to  rise  with  use,  it 
becomes  necessary  to  have  some  means  of  lowering  it  at  will. 
The  attachment  on  the  tube,  used  for  this  purpose,  is  illustrated 
by  D  in   Figure  3.     It  is   called  the  regenerator  or  regulator. 

A  small  elongation  projecting  from  the  top  of  the  hemi- 
sphere of  non-activity  is  packed  with  a  small  wad  ,of  asbestos. 
There  is  a  piece  of  platinum  wire  passing  into  the  elongation 
connected  with  the  exterior  cap  or  terminal.  To  operate,  we 
shunt  the  reduced  electrical  current  from  the  cathode  side  into 
the  regulator,  either  by  a  direction  connection  from  the  coil,  or 
by  causing  the  current  to  jump  from  the  external  cathode 
terminal  A  to  an  adjustable  wire  H,  attached  to  the  exterior 
regulator  terminal,  which  latter  is  brought  near  to  the  cathode 
terminal  when  we  wish  to  allow  some  current  to  be  shunted 
through  it.  The  current  passing  through  the  asbestos  generates 
heat  by  resistance,  which  in  turn  causes  the  asbestos  to  expand 
and  liberate  the  confined  air,  as  there  are  many  molecules  of 
air  held  entangled  in  the  porous  asbestos.  This  confined  air 
is  driven  off  into  the  tube  and  so  lowers  the  vacuum. 

This  is  a  very  desirable  form  of  regulator,  inasmuch  as 
we  utilize  it  zvith  the  current  passing  through  the  tube  and 
we  can  therefore  proceed  intelligently,  having  the  coloration 
in  the  tube  as  a  guide  to  the  extent  to  which  to  lower  it. 
When  we  reach  the  proper  shade  we  disconnect  the  wire  that 
is  carrying  the  current  to  the  regulator,  or  bend  up  the  wire 
attached  to  the  regulator  terminal  so  that  the  shunted  current 
no  longer  jumps  its  gap,  and  allow  it  to  pass  only  from  the 
main  cathode. 


48 


NOTES 


49 


50 


NOTES 


51 


NOTES 


52 


Figure  5 


Figure  6 


Figure  7     jti^^ 


^ 


fLRS.T'-. 


CHAPTER  VII. 
Symptoms  of  High  and  Low  Vacuum — Remedies  for  Same 

We  will  now  consider  the  symptoms  of  low  vacuum  and 
symptoms  of  high  vacuum,  and  the  remedies  for  these  defects. 
We  will  first  suppose  that  the  tube  is  working  properly,  with 
just  the  right  shade  of  green  to  give  us  a  good  dental 
radiograph  (Figure  5).  We  will  allow  a  heavy  electrical 
current  to  pass  through  the  tube  and  heat  up  the  metal  parts 
so  that  some  gas  will  be  driven  off,  causing  the  vacuum  to 
drop  a  little.  How  can  we  tell  when  the  vacuum  is  dropping? 
What  is  the  first  change  we  notice  ?  It  is  this :  we  note  first 
of  all  a  little  puff  of  blue  light  right  in  front  of  the  concave 
surface  of  the  cathode.  If  we  continue  to  lower  the  tube  this 
blue  puff  of  light,  which  resembles  very  much  a  little  puff  of 
smoke,  gradually  expands  in  the  form  of  a  cone,  the  apex  of 
which  extends  toward  the  surface  of  the  anode  (Figure  6). 
If  we  lower  it  still  more  this  blue  light  will  at  length  bridge 
the  gap  between  the  cathode  and  the  anode.  The  tube  is  then 
too  low  for  a  radiograph.  When  we  first  note  the  blue  light 
we  could  still  continue  to  take  a  radiograph,  but  it  is  a  danger 
signal  that  the  vacuum  is  going  down. 

The  first  thing,  therefore,  that  we  have  to  look  out  for  is 
the  appearance  of  blue  light  in  the  tube,  and  when  we  see  any 
indication  of  it  we  know  that  the  vacuum  of  the  tube  is  getting 
low.  We  must  be  careful  not  to  allow  the  vacuum  to  become 
TOO  LOW,  for  if  we  do  it  will  be  nearly  impossible  to  raise 
it  again.  By  the  time  that  the  blue  light  reaches  entirely  across 
the  tube  it  will  be  out  of  commission,  as  far  as  a  radiograph 
is  concerned.  Let  us  suppose,  nevertheless,  that  we  continue 
to  lower  the  tube  or,  rather,  let  us  suppose  that  the  tube  has 
become  punctured,  the  glass   wall   cracked,   and   therefore    the 

53 


air  from  the  outside  is  gradually  forcing  its  way  into  the 
tube.  We  will  follow  the  changes  that  take  place  in  the  tube 
until  the  air  on  the  outside  and  the  air  on  the  inside  have 
reached  equal  degrees  of  pressure.  From  the  time  when  the 
blue  light  reached  from  cathode  to  anode  we  find  that  it  will 
then  extend  and  spread  until  the  entire  tube  becomes  of  an 
even  bluish  color.  Next  we  will  note  a  little  puff  of  pink 
light  at  the  surface  of  the  cathode,  getting  denser  all  the  time 
in  color  until  it  finally  becomes  a  decided  red,  and  this  red 
also  takes  the  form  or  the  path  of  a  cone  and  travels  from 
the  cathode  to  the  anode.  It  will  then  expand  until  the  tube 
takes  on  a  red  coloration  which  indicates  that  the  vacuum  is 
very,  very  low.  The  next  change  we  note  is  that  this  red  coloration 
gradually  fades  away  until  we  see  absolutely  no  color  in  the 
tube,  but  instead  there  is  a  visible  spark  jumping  from  cathode 
to  anode.  When  we  see  this  we  know  that  the  vacuum  in  the 
tube  has  entirely  gone,  and  there  is  the  same  pressure  of  air 
inside  the  tube   as  outside. 

Let  us  now  consider  the  symptoms  of  high  vacuum.  Again, 
suppose  the  tube  to  be  working  properly,  with  just  the  right 
shade  of  olive  green.  What  will  be  the  first  sign  that  the 
vacuum  is  increasing?  First  the  shade  of  green  will  become 
lighter  and  lighter  with  an  ever-increasing  tendency  toward 
yellow.  Then  we  will  note  little  dancing  bright  yellow  spots 
of  light  throughout  the  tube,  not  confined  to  any  place,  but 
moving  around  (Figure  7).  At  first  there  will  be  just  a  few 
small  spots,  but  as  the  vacuum  increases  the  spots  get  larger, 
and  they  multiply  in  numbers  until  we  have  large  yellow  circles 
traversing  the  tube.  We  know  then  that  the  tube  is  very  high 
in  vacuum.  We  can  also  hear  a  crackling  noise,  caused  by  the 
static  discharge.  The  current  is  not  all  passing  through  the 
tube  as  it  should,  since  the  vacuum  of  the  tube  has  become 
too  great  for  all  the  current  to  pass  through;  therefore,  some 
of  the  current  passes  on  the  outside  and  follows  the  glass  wall 
of  the  tube.  When  these  yellow  circles  of  light  appear  in  the 
tube,   it   is   time    for   us   to   lower   the   vacuum.      If   when   we 

54 


first  place  the  tube  in  commission,  after  it  has  rested,  and  we 
note  the  yellow  spots  the  instant  we  turn  on  the  current,  do 
not  lower  the  vacuum  at  once,  but  let  it  run  for  a  few  seconds 
and  see  if  the  metals,  on  being  heated,  and  giving  off  gas,  will 
not  lower  the  vacuum  sufficiently.  If  this  is  not  the  case,  we  can 
then  resort  to  our  regulator  to  lower  the  vacuum.  Sometimes 
when  putting  on  a  new  tube,  or  one  that  has  been  used  a  great 
deal,  and  has  had  a  rest,  we  may  find  that  the  vacuum  is  so 
high  that  the  electrical  current  will  not  pass  through  it  at  all, 
but  instead  jumps  across  the  terminals  of  the  coil,  in  which 
case  it  should  be  lowered  at  once  by  the  regulator.  The  degree 
of  vacuum  is  often  referred  to,  as  governed  by  the  number  of 
inches  of  spark  it  will  'back  up*  on  the  coil.  To  test  this, 
start  the  tube  with  the  terminal  gap  wide  open  on  the  coil ;  now 
gradually  bring  the  terminals  together  till  the  current  starts  to 
jump  from  one  to  the  other,  instead  of  passing  through  the 
tube.     Measure  this  gap  in  inches. 

When  an  X  Ray  tube  has  become  too  low  there  is  nothing 
that  we  can  do  to  bring  it  up,  except  to  allow  a  very  small 
current  of  electricity  to  pass  through  it ;  in  the  opposite  direc- 
tion, so  that  we  barely  see  a  glow  in  the  tube.  Let  it  run  this 
way  for  some  time,  and  if  during  that  time  the  vacuum  does 
not  come  up  we  know  the  case  is  hopeless,  and  our  only  remedy 
is  to  send  it  to  the  manufacturer,  who  will  re-exhaust  it.  He 
will  break  the  'seal-off,'  through  which  the  gas  was  originally 
pumped  out,  and  will  let  the  air  into  the  interior,  and  again 
pump  it  out  to  the  right  degree  of  vacuum.  This  is  an  expensive 
process  and  it  is  better  to  prevent  the  tube  from  running  too 
low,  by  careful  watching,  and  avoid  the  re-exhausting  of  the 
tube. 

The  remedy  for  high  vacuum  is  simple,  but  we  must  be 
careful  not  to  lower  it  too  much.  A  tube  of  high  vacuum  has 
a  smaller  volume  of  rays  than  one  of  low  vacuum,  but  the  rays 
are  more  intense,  because  we  have  a  higher  potential  current 
forcing  its  way  through  the  high  vacuum.  The  volume  of  rays 
being    reduced    in    quantity,    and    the    intensity    being    greater, 

55 


therefore  the  velocity  with  which  the  rays  travel  will  be  greater. 
Again,  the  velocity  .being  greater  than  124  miles  per  second,  the 
bi-ultra  violet  rays  will  strike  the  platinum  anode  with  an 
increased  force  of  impact.  The  result  is  that  the  X  Rays  will 
be  broken  into  still  shorter  wave-lengths,  and  by  referring  to 
the  law  of  penetration,  the  shorter  the  wave  length  the  greater 
the  penetration;  therefore,  zve  have,  from  a  very  high  vacuum 
tube,  more  penetrative  power,  although  reduced  in  volume  or 
quantity. 

In  low  vacuum  tubes  the  entire  current  passes  through  it 
and  there  is  an  increased  volume  of  rays,  but  the  intensity  is 
not  as  great  because  the  rays  travel  with  a  lesser  velocity,  and 
the  rays  have  less  penetration. 

The  following  table  of  comparative  properties  of  high  and 
low  vacuum  tubes  should  be  carefully  studied,  as  a  thorough 
familiarity  with  these  properties  is  most  essential  to  the 
radiologist. 


56 


COMPARATIVE   TABLE   OF   HIGH   AND   LOW 
VACUUMS 


HIGH   VACUUM   TUBES 
(Sometimes   called   'hard' 
tubes.) 

Electrical  discharge  or 
'static'  on  outside  of  tube. 

Coloration  tending  toward 
yellow,  with  bright  yel- 
low in  places.  (Remedy: 
lower  vacuum  with  the 
regulator.) 

Less  volume,  or  quantity  of 
X  Rays. 

More  penetrating  X  Rays. 

Less  contrast  between 
blacks  and  whites,  in 
radiograph. 

More  exposure  needed  as 
compared  with  medium 
vacuum  tubes,  due  to  lack 
of  volume   of  rays. 

Low  milliamperage  i  n 
secondary   circuit. 

Less  danger  of  dermatologi- 
cal  effects,  due  to  greater 
penetration  and  less  ab- 
sorption of  X  Rays  by  the 
superficial  tissues. 

Glass  wall  of  tubes  more  apt 
to  puncture. 

Surface  of  anode  less  apt  to 
burn  out. 


LOW    VACUUM    TUBES 
(Sometimes    called    'soft' 
tubes.) 

No  electrical  discharge  or 
'static'  on  outside  of  tube. 

Coloration  tending  toward 
blue-green  with  blue 
pufifs  of  light  in  places. 
(Remedy:  give  tube  a 
rest,  or  reverse  current  on 
reduced  potential.) 

Greater  volume,  or  quantity 
of  X  Rays. 

Less  penetrating  X  Rays. 

More  contrast  between 
blacks  and  whites  in  radio- 
graph. 

More  exposure  needed  as 
compared  with  medium 
vacuum  tubes,  due  to  lack 
of  penetration   in   X  Rays. 

High  milliamperage  in  sec- 
ondary circuit. 

More  danger  of  dermatolo- 
gical  effects,  due  to  less 
penetration  and  more  ab- 
sorption of  X  Rays  by  the 
superficial   tissues. 

Glass  wall  of  tubes  less  apt 
to  puncture. 

Surface  of  anode  more  apt  to 
burn  out. 


57 


NOTES 


58 


CHAPTER  VIII. 

The  Essentials  of  an  Outfit — Methods  of  Generating  High  Potential 
Electric  Currents — Electrical  Measurements 

There  are  four  essential  parts  of  an  X  Ray  outfit  for  the 
dentist.  First,  the  induction  coil,  or  other  means  of  obtaining 
our  high  potential  current;  second,  the  interrupter  (providing 
an  induction  coil  is  used)  ;  third,  the  X  Ray  tube;  and  fourth, 
the  X  Ray  'tube-shield.'  This  last  piece  of  apparatus  is 
essential  to  the  health  and  protection  of  the  operator,  and  not 
to  the  working  of  the  apparatus,  but  it  is  so  important  that 
we  class  it  as  one  of  the  four  essential  parts  of  the  outfit. 

There  are  four  methods  in  general  use  for  the  generating 
of  the  high  potential  current;  we  will  consider  them  in  the 
order  of  their  efficiency. 

First,  the  'motor-generator-transformer'  type,  commonly 
known  as  the  'interrupterless,'  with  a  maximum  output  of 
110,000  volts,  and  as  high  as  200  milliamperes. 

Secondly,  the  induction  coil,  with  a  maximum  output  of 
about  120,000  volts  in  a  12-inch  coil,  but  with  a  milliamperage 
of  from  15  to  30. 

Thirdly,  the  static  machine,  with  a  maximum  output  of 
about  200,000  volts  in  one  of  the  largest  machines,  and  about 
2^  to  5  milliamperes. 

Lastly,  the  Tesla  transformer,  with  an  average  maximum 
output  of  about  60,000  volts,  and  only  1  or  2  milliamperes. 

We  will  consider  the  types  that  we  have  mentioned,  taking 
up  first  the  most  efficient,  the  'interrupterless'  type.  This  is 
an  apparatus  that  represents  the  very  latest  achievement  of  the 
manufacturers.  It  is  a  type  of  apparatus  that  enables  us  to  do 
instantaneous  work  in  radiography.  We  will  describe  the  con- 
struction of  it  very  briefly. 

59 


Figure  8 — (see  page  62) 

60 


If  the  direct  current  is  the  source  of  supply,  then  a. rotary 
converter  is  used  to  produce  an  alternating  current  from  the 
direct  current.  The  motor  set  consists  of  a  rotary  converter  on 
the  direct  lighting  circuit,  either  220  or  110  volts.  The  rotary 
converter  changes  the  direct  current  into  an  alternating  and 
passes  it  through  the  necessary  switch,  on  the  switchboard,  and 
the  rheostat  to  the  transformer.  On  the  end  of  the  shaft  of  the 
motor  is  attached  a  round  micanite  disk.  The  low  potential 
alternating  current  collected  from  the  converter  side  is  passed 
through  the  primary  of  the  transformer  which  increases  its 
potential  to  about  100,000  volts  "at  a  primary  current  of  from 
25  to  50  amperes,  depending  on  voltage  used.  The  high  poten- 
tial alternating  current  is  then  conducted  from  the  transformer 
to  a  rotary  polechanger,  mounted  on  the  armature  shaft  of 
the  converter. 

The  rotary  polechanger  consists  of  a  round  micanite  disk. 
To  the  periphery  of  this  disk  are  fastened  two  copper  strips, 
opposite  each  other,  and  occupying  a  little  more  than  a  quarter 
of  the  circumference.  Parallel  to  this  disk  is  a  glass  plate,  on 
which  are  mounted  four  contact  brushes  equidistantly  apart. 
They  are  arranged  to  commutate,  or  rectify  the  current 
from  a  high  tension  alternating,  to  a  high  tension,  interrupted 
unidirectional  current.  The  alternating  current  enters,  as  it 
were,  at  two  opposite  contacts,  and  the  rectified  current  is 
taken  from  the  two  remaining  contacts  and  conducted  to  the 
outlet  terminals. 

The  great  efficiency  and  superiority  of  this  type  of  appa- 
ratus lie  not  in  its  high  potential,  which  is  less  than  some  of 
the  larger  types  of  coils,  but  is  due  to  the  great  increase  of 
current  strength,  or  milliamperage,  together  with  the  fact  that 
the  current  derived  is  unidirectional,  thus  cutting  out  all 
'inverse'  in  the  tube.  These  outfits  are  very  expensive  and  their 
use  is  adapted  to  the  needs  of  the  specialist  who  intends  to  take 
up  general  radiology  as  a  profession,  and  practice  it  in  all  its 
varied  fields  and  applications.  To  the  specialist,  therefore,  the 
interrupterless    type    is    not    an    extravagance,    but    is    really    a 

61 


necessity.  Figure  8  represents  the  ''King  model"  type  of  inter- 
rupterless  outfit,  manufactured  by  the  Wappler  Elec.  Mfg.  Co. 
of  New  York  City.  It  is  without  doubt  the  'last  word"  in 
X  Ray  outfits. 

The  next  type  of  apparatus,  the  induction  coil,  is,  on  the 
whole,  used  more  than  any  other  type  of  apparatus.  It  is  much 
less  costly  than  the  'interrupterless'  and  fulfils  the  need  of  the 
average  practitioner,  in  fact  many  specialists  do  all  their  work 
with  a  good-sized  coil.  In  its  latest  form  it  is  admirably  suited 
to  the  dental  surgeon,  and  is  more  appropriate  for  his  use  than 
the  larger  and  more  expensive  interrupterless  kind.  Figure  9 
illustrates  the  very  latest  type  of  X  Ray  coil,  designed  especially 
for    dental    work.  With    it,    any    dentist    can    well    com- 

pete with  the  specialist  and  his  interrupterless  outfit.  It  is  not 
only  thoroughly  efficient,  but  is  much  lower  in  cost  than  any 
other  types  of  coil,  and  occupies  the  minimum  of  floor  space 
in  the  dental  office.  It  presents  a  truly  scientific  and  aseptic- 
looking  piece  of  apparatus.  It  is  made  by  the  American  X  Ray 
Equipment  Co.  of  New  York  City.  For  the  present  we  will 
pass  over  the  description  of  the  induction  coil  and  consider  the 
other  two  types. 

The  third  type  of  apparatus  is  the  static  machine,  the  use 
of  which  is  becoming  more  obsolete  every  day.  It  is  the  only 
one  of  the  four  methods  of  generating  the  current  for  the 
X  Ray  tube  in  which  the  current  is  generated  directly  from 
friction  and  not  stepped  up  from  a  low  potential  current  as  in 
the  cases  of  the  other  three.  In  the  static  machine  we  have 
large  wheels  of  glass  revolving  with  metallic  disks  fastened  to 
their  surface  at  various  intervals.  These  disks  revolve  against 
wire  brushes  and  by  means  of  the  friction  that  is  developed 
and  the  great  speed  with  which  they  are  revolving,  generate 
frictional  electricity.  This  electrical  current  is  picked  up  and 
magnified  by  each  revolution  until  it  is  delivered  from  con- 
densing leyden  jars,  to  the  terminals  of  the  apparatus  as  a 
high  potential  static  current.  Small  static  machines  are  of 
very   little   value   to   the    radiologist,    and   the    larger    ones    are 

62 


The  Standard 
Dental  Outfit 
American  X  Ray 
Equipment  Co. 


Figure  9 — (see    page   62) 
63 


Figure  10 — (see  page  65; 


64 


very  expensive,  even  more  expensive  than  the  highest  type  of 
interrupterless  apparatus  and  with  an  efficiency  proportionately 
less.  Figure  10  represents  the  latest  and  most  improved  model 
of  static  machine,  made  by  Waite  &  Bartlett  Co.  of  New 
York  City. 

The  last  type,  the  Tesla  transformer,  is  at  the  present 
time  less  efficient  than  the  other  three  types,  but  it  has  one 
advantage  of  being  the  most  portable,  a  complete  Tesla  coil 
that  will  generate  a  high  potential  current  sufficient  to  taking  a 
radiograph,  can  be  carried  readily  in  a  dress-suit  case  and  weighs 
only  about  twenty  or  thirty  pounds.  Such  a  piece  of  apparatus 
will  give  us  a  radiograph  in  from  thirty  seconds  to  a  minute,  a 
rather  long  time  for  the  patient  to  remain  still,  but  not  impos- 
sible. It  is  less  expensive  than  any  of  the  others,  and  is  to  be 
recommended  to  those  men  who  desire  to  get  an  outfit  for  as 
small  amount  of  money  that  will  enable  them  to  do  some  X  Ray 
work  as  an  adjunct  to  their  profession.  It  is  a  good  starter 
for  the  man  with  the  small  purse  and  probably  will  be  the 
forerunner  of  larger  and  more  elaborate  apparatus. 

A  very  complete  and  compact  Tesla  type  of  dental  outfit  is 
being  placed  on  the  market  as  this  book  goes  to  press,  and 
from  tests  made  with  it  bids  fair  to  being  a  very  efficient  model 
of  a  low-priced  outfit;  it  is  also  made  by  the  American  X  Ray 
Equipment  Co.  of  New  York  City. 

We  will  now  go  back  to  the  induction  coil,  its  principles 
and  construction,  and  methods  of  generating  the  high  potential 
current. 

The  current  that  we  use  in  X  Ray  work  is  a  high  potential 
current,  and  by  potential  we  mean  electro-motive  force  or 
voltage.  We  must  have  a  current  of  high  voltage.  If  we 
attach  our  X  Ray  tube  directly  to  the  street  current  service 
wires,  or  to  the  wires  from  a  battery  we  would  have  no  result. 
The  current  would  not  pass  through  the  tube.  The  reason  for 
this  is  that  the  vacuum  offers  too  great  a  resistance ;  to  a  low 
potential  current  the  vacuum  is  an  absolute  non-conductor. 
Therefore  a  current  that  we  can  force  through  an  X  Ray  tube 

65 


must  be  of  at  least  50,000  volts.  Let  us  see  how  we  generate 
this  current  in  an  induction  coil. 

An  induction  coil  consists  of  two  principal  parts,  each  one 
a  separate  coil  of  wire.  The  first  coil  has  but  a  few  turns  of 
very  coarse  wire  (for  an  X  Ray  coil  it  must  be  of  8,  10,  12 
or  14  gage  wire),  wrapped  around  a  bundle  of  soft  iron  wire 
which  forms  the  magnetic  core  of  the  coil.  This  first  coil  is 
called  the  'primary'  coil.  The  second  coil  is  called  the  'secondary' 
coil,  and  consists  of  a  great  many  turns  of  very  fine  wire 
(usually  number  thirty-four  silk-insulated  wire  is  used  in  the 
secondary). 

Before  taking  up  the  physics  of  the  induction  coil  let  us 
first  review  some  of  the  elementary  principles  of  electricity,  that 
we  may  have  a  clearer  understanding  of  the  operation  of  the 
coil. 

What  is  electricity?  We  do  not  know  absolutely;  we  do 
know,  however,  that  it  is  a  form  of  energy  that  is  invisible. 
At  one  time  it  was  believed  to  be  a  liquid  that  was  invisible, 
and  that  it  permeated  all  substances,  for  the  reason  that  its 
action  followed  so  closely  the  laws  of  liquids.  Therefore  we 
very  often  use  similes  in  hydrostatics  (the  laws  of  liquids  at 
rest)  and  hydrodynamics  (the  laws  of  liquids  in  motion),  to 
explain  the  phenomena  occurring  in  electrical  science.  Even 
though  the  exact  nature  of  this  invisible  force  or  form  of 
energy,  which  we  call  electricity,  is  unknown,  we  are  able  to 
measure  it.  Instruments  have  been  devised  that  will  tell  us  just 
how  much  of  this  force,  and  to  what  extent  it  is  being  used. 
It  was  necessary  before  we  could  do  this,  to  originate  certain 
units  of  measurement,  just  as  we  have  units  of  measurement 
for  weight,  for  time,  and  for  volume. 

The  first  unit  of  measurement  is  the  'volf  which  may  be 
defined  as  the  unit  of  electro-motive  force.  This  tells  us  very 
little  until  we  know  what  electro-motive  force  is,  and  to  explain 
that  we  will  consider  a  simple  simile : — 

Suppose  a  tank  of  water  is  situated  upon  the  roof  of  a 
tall  building.     Froiji  this  tank  of  water  we  have  a  pipe  leading 

66 


down  to  the  ground  floor,  which  can  be  tapped  at  all  the  inter- 
mediate floors  to  furnish  the  people  in  the  house  with  water. 
At  the  ground  floor  there  is  a  greater  pressure  than  at  the 
top  floor;  the  tenants  at  the  top  of  the  house  do  not  get  as 
great  a  force  of  water  as  those  living  on  the  first  floor,  because 
of  the  weight  of  the  water  in  the  pipe,  together  with  the  laws 
of  falling  bodies,  which  materially  adds  to  the  pressure,  or  the 
head  of  water,  at  the  lower  level.  This  water  pressure  is 
analogous  to  voltage  in  an  electrical  current. 

The  unit  of  measurement  of  electro-motive  force  means 
the  unit  of  pressure.  It  is  the  amount  of  electricity  measured 
in  its  potential,  its  power,  its  intensity  or  tension.  In  the  case 
of  the  tank,  the  higher  the  tank  is  from  the  street  the  greater 
will  be  the  potential,  or  the  greater  will  be  the  force;  and  that 
force  may  be  likened  to  the  power  that  sets  electricity  in  motion. 

Now  suppose  we  have  two  pipes  coming  down  from  this 
tank,  one  a  half  inch  in  diameter  and  the  other  one  two  inches 
in  diameter.  Which  will  discharge  the  most  water?  The 
two-inch  pipe  you  will  say  discharges  more  water.  That  is 
true,  but  it  does  not  come  with  as  great  a  force  from  the  two- 
inch  pipe  as  it  does  from  the  half -inch  pipe.  You  have  probably 
noticed  that  with  a  garden  hose,  if  you  press  the  nozzle  to- 
gether, you  can  throw  the  water  to  a  greater  distance.  You 
have  increased  the  pressure.  This  pressure  is  analogous  to 
voltage  in  an  electrical  current. 

The  quantity  of  water  passing  through  the  pipe  in  a  given 
time,  that  is,  the  number  of  gallons  per  hour,  is  analogous  to 
the  second  unit  of  measure  for  electrical  currents,  called  the 
'ampere.'  The  definition  of  the  ampere  is,  the  unit  of  current- 
strength;  in  other  words,  it  is  the  amount  of  current  passing 
a  given  point  on  a  conductor  in  a  given  time.  You  see,  there- 
fore, the  difference  between  volts  and  amperes.  The  volt 
represents  the  intensity  of  the  current,  and  the  ampere  repre- 
sents the  Yate  of  current-flow.  One  only  exists  at  the  expense 
of  the  other.  Just  as  we  have  pressure  and  quantity  in  water, 
if  we  increase  the  pressure  in  the  garden  hose,  we  throw  the 

67 


water  a  greater  distance,  but  we  do  not  deliver  as  much  water 
in  the  same  time.  If  we  increase  the  diameter  of  the  pipe  and 
allow  more  water  to  pass  it  is  not  thrown  to  as  great  a 
distance;  the  pressure  is  less.  One,  therefore,  exists  at  the 
expense  of  the  other. 

The  third  unit  of  measurement  that  we  have  to  consider, 
is  the  unit  of  resistance  called  the  'ohm.'  It  would  be 
analogous  in  our  water  pipe  to  the  number  of  curves  and  bends 
and  to  the  friction  of  the  water  against  the  side.  It  is  the 
resistance  that  the  column  of  water  has  to  meet  with,  and  in 
electrical  currents  it  is  the  resistance  of  a  poor  conductor 
which  absorbs  some  of  the  electricity  and  converts  it  into 
another  form  of  energy  which  we  know  as  heat.  If  it  were 
not  for  resistance  we  would  have  no  incandescence  in  electric 
lamps.  The  ohm  is  the  actual  resistance  offered  to  an  electrical 
current  by  150  feet  of  copper  wire,  one  millimeter  in  diameter, 
or  it  is  the  resistance  offered  by  a  column  of  mercury  one  meter 
in  height  and  with  a  diameter  of  one  millimeter. 

We  have  considered  the  three  practical  units  of  electrical 
measurement,  viz.,  the  volt,  the  ampere  and  the  ohm.  The 
volt  or  the  unit  of  electro-motive  force,  the  ampere,  the  unit 
of  current  strength,  and  the  ohm,  the  unit  of  resistance.  One 
of  the  fundamental  laws  upon  which  all  electrical  science  is 
based  is  known  as  Ohm's  Law.     The  formula  is  this : 

C  equals  E  divided  by  R.    (C=— .) 

R 

In  this  formula  C  stands  for  current  or  amperes;  E  stands 
for  electro-motive  force  or  volts ;  R  stands  for  resistance  or 
ohms,  so  that  we  may  write  that  same  law  in  another  way: 
Amperes  equal  volts  divided  by  ohms. 

From  this  law,  which  is  in  the  form  of  an  equation,  we 
can  find  any  unit  provided  we  have  the  other  two  units  given; 
for  example,  we  will  take  a  simple  problem:  How  many 
amperes  will  pass  through  an  electrical  lamp  operating  under  a 
potential    of    110   volts    and    with    a    resistance    of    220   ohms? 

68 


Applying  the  formula,  it  will  read  this  way:  X  equals  110 
divided  by  220.  X  being  the  amperes  that  we  wish  to  find, 
110  representing  the  voltage  passing  through  the  lamp  and  220 
representing  the  ohms  of  resistance  to  that  current.  Reducing 
this  fraction  to  its  lowest  terms,  we  see  that  it  equals  ^-2 ; 
therefore,  we  have  Yi  an  ampere  of  current.  By  transposing 
Ohm's  Law  formula  we  have 

E=RXC,   and   R=^ 


69 


NOTES 


70 


NOTES 


71 


Ga-lvanometer 


X^ 

SECONDARY 

^^ 

^  Y 

Mr 

PRIMARY 

r-^ 

T 

B&»tetjjCe\l. 

Swi"l:cK, 

fLRSji 

Figure    11  — (see  page  73) 


n 


CHAPTER  IX. 
Electrical  Induction — Construction   of  X   Ray   Coils 

Let  MN  (in  Figure  11)  represent  a  straight  wire  connected 
at  both  ends  with  a  battery,  and  let  XY  also  represent  another 
wire  that  is  near  to  and  parallel  with  the  first  wire,  and  con- 
nected at  both  ends  to  a  galvanometer.  We  have,  therefore,  two 
separate  and  distinct  circuits,  the  first  made  up  of  the  wire 
MN,  the  battery  B  and  the  switch  S,  which  we  will  call  the 
'primary'  circuit.  The  other  circuit  consisting  of  the  wire  XY, 
which  is  of  equal  length  and  thickness  as  MN  and  the  galvano- 
meter G,  which  will  record  the  presence  and  comparative 
intensity  of  electrical  impulses. 

We  will  now  "make"  the  primary  circuit,  in  other  words, 
close  the  switch  and  allow  a  current  of  electricity  to  pass 
through  the  wire  MN.  At  the  instant  that  the  current  passes 
through  the  wire  MN,  a  single  impulse  is  generated  in  the 
secondary  circuit,  or  the  wire  XY,  which  lasts  but  for  a  single 
instant,  as  shown  by  the  deflection  of  the  galvanometer  needle, 
we  will  say,  two  points  to  the  right  and  its  immediate  return  to 
*0.'  There  is  no  more  current  passing  through  XY,  although 
the  current  continues  to  pass  through  MN.  When  we  "break" 
the  current  that  is  passing  through  MN  (open  the  switch)  and 
cause  it  to  stop  flowing,  we  will  have  another  current  generated 
in  XY,  but  flowing  in  the  opposite  direction,  as  shown  by  the 
galvanometer  needle  deflecting  two  points  to  the  left.  This  also 
will  be  but  an  instantaneous  impulse  and  then  it  will  stop. 
This  phenomenon  is  known  as  induction  and  always  takes  place 
where  we  have  a  conductor  in  the  neighborhood  of  another 
conductor,  and  when  there  is  a  current  of  electricity  passing 
through  the  former.     Induction  takes  place  at  its  maximum,  or 

7Z 


we  say  the  inductiveness  is  at  its  maximum  when  the  neighbor- 
ing conductor  is  parallel  with  the  original  conductor.  If  the 
neighboring  conductor  was  at  right  angles  to  the  one  that  the 
current  was  passing  through,  we  would  have  no  impulse,  and 
it  would  vary  from  nothing  to  maximum  as  we  swing  the 
angle  round  through  the  quadrant  of  90  degrees.  The  same 
phenomenon  takes  place  in  the  induction  coil.  We  pass  a  cur- 
rent of  electricity  through  the  primary  coil  and  a  current  is 
induced  in  the  secondary  coil,  the  layers  of  which  are  parallel  to 
each  other.  There  is  no  connection  between  the  two  coils.  They 
are  both  separate  and  distinct,  yet  a  current  is  induced  in  the 
secondary  coil  when  the  current  in  the  primary  is  started  and 
when  it  is  stopped.  If  the  windings  of  the  primary  consisted 
of  but  a  single  layer  with  a  given  number  of  turns  and  the 
windings  of  the  secondary  consisted  also  of  but  a  single  layer, 
with  the  same  number  of  turns,  the  potential  of  the  secondary 
would  be  the  same  as  the  primary,  the  voltage  would  not  be 
increased,  but  if  we  increase  the  number  of  turns  in  the 
secondary  we  get  an  increase  of  potential  which  is  caused  by 
the  phenomenon  of  self-induction;  in  other  words,  each  turn 
of  the  secondary  induces  a  current  in  the  turn  directly  adjacent 
which  must  be  added  to  the  induction  that  is  caused  from  the 
primary  current,  so  that  in  the  first  layer  of  the  secondary,  if 
it  had  ten  times  the  number  of  turns,  the  potential  would  be 
ten  times  as  high  as  the  primary;  in  the  next  layer  it  is  the 
same  as  the  first  layer,  plus  the  extra  induction  of  the  current 
flowing  through  the  additional  number  of  turns  in  the  second 
layer  of  the  secondary;  in  the  third  layer  it  is  still  higher, 
because  the  effects  of  the  first  two  layers  are  added  to  the  effect 
of  the  primary,  and  so  on,  through  all  the  layers  of  the 
secondary  coil.  If  we  consider  the  number  of  layers  and  the 
number  of  turns  that  the  secondary  wire  takes  in  the  length 
of  about  twenty-eight  miles  (which  is  about  the  length  of  the 
secondary  of  a  12-inch  induction  coil)  you  can  readily  see  that 
we  are  adding  an  enormous  quantity  of  potential  to  the  original 
current  flowing  through  the  primary  coil. 

74 


As  the  voltage  was  increasing  the  amperage  was  decreasing 
with  an  equal  ratio.  The  wire  was  very  fine  in  the  secondary, 
offering  great  resistance  to  the  passage  of  the  electrical  current ; 
consequently  the  rate  of  flow  or  amperage  must  be  decreased 
as  the  potential  increases,  so  that  the  output  from  the  secondary 
coil  would  be  perhaps  120,000  volts  and  about  ten  one-thou- 
sandths of  one  ampere,  or  10  milliamperes.  If  we  compare  the 
original  current  in  the  primary  of  110  volts  (and  we  will  say  30 
amperes),  we  will  see  that  nothing  is  changed  in  value,  only 
the  form  of  the  current  has  been  transformed.  It  is  the  same 
case  as  though  you  took  a  ten-dollar  bill  to  the  bank  and 
exchanged  it  for  ten  one-dollar  bills.  We  have  no  more  value 
than  we  had  before,  but  we  have  it  in  a  different  form,  so 
that  it  can  do  a  certain  class  of  work  which  we  wish  it  to 
perform,  where  the  other  one  would  not.  We  have  not  created 
any  new  energy. 

The  following  table  shows  six  manipulations  of  the  primary 
circuit  that  give  us  impulses  in  the  secondary.  Let  us  carefully 
examine  the  table. 

TABLE   OF   PRIMARY   MANIPULATIONS    GIVING 
SECONDARY  EFFECTS 


SKCONDARY    EFFECTS 


INVERSE 

—  to  -f 


DIRECT 

-f   to  - 


PRIMARY    MANIPULATIONS 


—2  Make 

— 1  Approached 

— 4  Increase  of  potential. 


+2  Break. 

-j-1  Withdrawn. 

4-4  Decrease  of  potential. 


Under  the  heading,  'secondary  effects,'  we  will  see  the 
words  inverse  and  direct ;  inverse  meaning  a  current  flowing 
from  negative  to  positive,  and  direct,  a  current  flowing  from 
positive  to  negative.  In  the  two  columns  below  we  will  find  the 
manipulations  of  the  primary  coil  that  give  us  these  effects  in 

75 


the   secondary;   in   other   words,   the   causes    for   these   effects. 
There  are  six  causes   altogether,   or  six  manipulations   of  the 
primary  that  give  us  effects  in  the  secondary.     The  first  two 
are  'make'  and  'break.'     We  will  find  in  the  first  column  'make' 
and  in  the  next  column  'break.'     This  means  that  if  you  'make' 
the   primary,    or    start   the   current    flowing,    you    get    a    single 
impulse  in  the  secondary  which  is  'inverse'  in  direction.     When 
you    'break'    the    primary    you    get    a    single    impulse    in    the 
secondary  that  is  'direct'  in  direction.     The  next  two  manipula- 
tions   of    the    primary    are    the    'approached'    and    'withdrawn' 
currents.     We  see  in  the  first  column  'approached'  and  in  the 
second  column  'withdrawn.'     In  order  to  explain  the  meaning 
of  the  'approached'  and  'withdrawn'  currents,  we  will  have  to 
suppose  that  we  have  a  small  induction  coil,  operating  with  a 
battery  and  not  from  the  street  current,  and  having  a  primary 
that  is  removable;  that  is,  the  primary  coil  may  be  drawn  out 
from  the  core  where  it  rests   inside  the  secondary.     We   will 
'make'  the  current  in  the  primary.     We  get  a  single  impulse  in 
the  secondary  and  then  there  is  no  more  current  flowing.     The 
secondary  circuit  for  the  time  being  is  'dead,'  although  the  cur- 
rent continues  to  flow  in  the  primary.     Now  if  we  take  hold  of 
the  primary  coil  and  suddenly  pull  it  out  from  the  core,  where 
it  rests  in  the  secondary,  we  get  an  impulse  in  the  secondary 
circuit  just  as  though  we  'broke    the  primary  current.     Again 
quickly  replacing  the  primary  back  into  the  secondary,  we  get 
another    impulse   which    is    'inverse'    in   the    secondary.         The 
'approached'  and  'withdrawn'  currents  are  obtained,  therefore, 
by  altering  the  relative  distances  between  the  primary  and  the 
secondary  coils,  either  approaching  the  primary  to  the  secondary 
or  the  removing  of  the  primary  from  the  secondary.     The  next 
two   ways   of   obtaining  impulses   in  the  secondary  are  by  the 
'increase'  and  'decrease  of  potential'     In  the  first  column  we 
find  'increase  of  potential,'  and  in  the  second  column  'decrease 
of  potential.'    We  mean  by  'increase'  and  'decrease  of  potential' 
the  increasing  of  the  voltage  and  the  decreasing  of  the  voltage 
of  the  primary   circuit.      Suppose,   in   the   small   induction   coil 

76 


that  we  just  referred  to,  that  we  had  a  switch  by  means  of 
which  we  could  throw  in  the  current  from  six  dry  cells  in 
addition  to  a  battery  of  ten,  which  we  had  originally.  We  first 
'make'  the  current  with  the  battery  of  ten  dry  cells.  We  get 
one  impulse  in  the  secondary  at  the  'make.'  Now  with  the  cur- 
rent still  flowing  in  the  primary  with  a  potential  of  10  volts 
(each  dry  cell  giving  approximately  1  volt),  we  throw  in, 
without  breaking  the  circuit,  an  additional  supply  of  voltage 
from  the  six  extra  dry  batteries.  We  therefore  have  an  'increase  of 
potential'  in  the  primary  circuit.  The  voltage  is  raised  from 
10  to  16.  At  the  instant  that  this  takes  place  we  have  an 
impulse  in  the  secondary  which  is  'inverse'  in  direction.  Again, 
if  we  were  suddenly  to  cut  out  six  dry  cells  we  would  decrease 
this  voltage  from  16  to  10,  and  we  would  get  an  impulse  which 
would  be  'direct.'  These  are  the  six  methods  of  obtaining 
impulses  in  the  secondary,  and  they  are  the  only  ways  by  which 
we  can  get  secondary  impulses;  but  they  are  not  all  equal  to 
each  other. 

Let  us  suppose  that  we  have  an  induction  coil  without  any 
internal  resistance  (which  is  impossible,  although  coils  may  be 
constructed  coming  pretty  close  to  it),  also  let  us  suppose  we 
have  a  sensitive  galvanometer  in  the  secondary  circuit.  We  will 
'make'  the  primary,  and  show  the  impulse  passing  in  the 
secondary  by  a  deflection  on  the  galvanometer.  We  will  sup- 
pose that  it  deflects  two  points  to  the  left.  We  will  put  down, 
therefore,  opposite  the  word  "make"  the  figure  2,  and  since 
it  gives  us  the  inverse  discharge,  we  will  mark  it  minus  ( — ). 
When  we  'break'  the  current  we  would  get  a  deflection  in  the 
galvanometer  of  two  points  on  the  other  side,  provided,  of 
course,  the  coil  was  without  resistance;  the  needle  having 
come  back  to  zero  would  swing  over  to  two  points  on  the  right 
side  and  register  the  single  impulse  and  then  comes  back  again 
to  zero.  We  will  put  down  opposite  the  word  "break"  this 
figure  2,  with  the  plus  (  +  )  sign  before  it,  because  it  represents 
a  direct  current  'flowing  in  the  secondary.  In  the  case  of  the 
approached    and    withdrawn    current    the    galvanometer    might 

77 


show  only  a  deflection  of  one  volt.  We  therefore  put  down  the 
value,  one,  in  both  columns,  with  the  minus  ( — )  on  one  side 
and  the  plus  (  +  )  on  the  other.  That  means  that  the 
impulse  of  the  'approached'  and  the  'withdrawn'  was  only, 
in  this  case,  one-half  as  great  as  the  impulse  of  the  'make'  and 
the  'break.'  Now  the  impulse  of  the  'increase  of  potential'  and  'de- 
crease of  potential'  may  be  twice  as  great  as  the  'make'  and  the 
'break,'  depending  on  the  amount  of  'increase'  and  'decrease;' 
therefore,  the  galvanometer  would  show,  we  will  say,  in  this  case 
a  deflection  of  four  points  to  the  left  and  to  the  right,  according 
as  we  'increase'  and  'decrease  the  potential.'  We  will  put  down, 
therefore,  a  value  of  minus  ( — )  4  for  the  'increase  of  potential' 
and  a  value  of  plus  (  +  )  4  for  the  'decrease  of  potential.'  Now, 
therefore,  we  have  in  this  case  a  ratio  of  'one  is  to  two  is  to 
four.'  This  ratio  is  not  ahvays  constant,  but  depends  on  several 
controlling  factors;  neither  do  we  ever,  in  practice,  have  the 
inverse  impulses  equal  to  the  direct  impulses.  They  are  always 
greater. 

The  current  that  we  use  in  the  X  Ray  tube,  that  is,  the 
high  potential  secondary  current,  entered  the  tube  at  the 
negative  or  the  cathode  side;  it  passed  through  the  tube  and 
out  again  at  the  anode  or  the  positive  side  of  the  tube.  This 
was,  consequently,  what  we  term  an  'inverse  current'  flowing 
from  negative  to  positive.  This  'inverse  current'  is  obtained 
from  the  secondary  of  the  induction  coil  at  the  'break'  of  the 
'primary,'  and  yet  by  looking  at  the  table  we  see  that  the 
'break'  of  the  primary  should  give  us  a  'direct'  current  in  the 
secondary.  This  apparent  discrepancy  takes  place  because  we 
have  two  factors  taking  place  at  identically  the  same  instant. 
At  the  instant  that  we  get  our  'break'  in  the  primary,  we  also 
get  an  'increase  of  potential'  (produced  automatically  in  the 
interrupter,  which  we  will  consider  later),  both  taking  place 
absolutely  simultaneously.  We  have,  therefore,  the  effect  of 
a  plus  value,  which  was  that  of  the  'break,'  and  the  effect  of 
minus  value,  which  was  that  of  the  'increase  of  potential,'  to 
be  added.     This  latter  value  ahvays  exceeding  the  former,  and 

78 


in  the  case  of  large  X  Ray  coils  and  electrolytic  interrupters 
the  intensity  of  the  'increase  of  potential'  effect  is  sometimes 
twenty  or  thirty  times  as  great  as  the  'make'  and  'break'  effects. 
The  result  being  a  predominance  of  the  effect  of  the  'increase 
of  potential'  over  that  of  the  'break,'  giving  us  as  a  result  an 
increased  potential  current,  'inverse'  in  direction,  at  the  instant 
of  the  'break/  The  'increase  of  potential'  had  a  greater  effect 
on  the  secondary  than  the  'break,'  but  as  they  were  opposite 
effects  the  stronger  is  going  to  predominate   over  the   weaker. 

In  the  construction  of  an  induction  coil  for  X  Ray  work 
we  must  have  a  'primary'  that  is  removable  from  the  'second- 
ary.' This,  because  it  may  be  necessary  to  make  a  repair  on 
the  'primary,'  due  to  the  short  circuiting  of  the  current.  It 
would  be  inconvenient  to  unwind  a  great  many  miles  of  wire  in 
order  to  get  at  the  'primary'  to  make  a  repair,  and  it  is  there- 
fore easier  to  construct  the  coil  originally  so  that  the  'primary' 
may  be  removed.  Another  requisite  of  a  good  coil  for  X  Ray 
work  is  a  thoroughly  insulated  'secondary/  This  is  obtained  by 
winding  the  secondary  coil  in  two  or  more  segments.  The 
segments  are  insulated  from  each  other  and  all  boiled  separately 
in  a  composition  wax.  Afterward,  when  they  are  placed  in 
the  case  that  will  enclose  them,  and  their  terminals  joined,  the 
entire  case,  which  is  to  form  the  finished  coil,  is  filled  with  the 
same  melted  wax  composite.  This  is  the  best  form  of  insula- 
tion. If  a  current  should  jump  from  one  layer  to  the  other  in 
the  'secondary,'  caused  by  a  'breakdown'  of  the  silk  insulation, 
the  wax  in  contact  would  also  be  melted  by  the  heat  generated, 
the  melted  wax  would  flow  over  the  bad  part  of  the  wire  and 
would  reinsulate  it.  These  are  the  two  principal  features  of  the 
construction  of  the  coil. 

An  X  Ray  coil  has  no  vibrating  interrupter  attached  to 
it  as  part  of  the  apparatus.  In  X  Ray  work  the  interrupter 
forms,  a  separate  and  distinct  piece  of  apparatus,  the  'coil'  itself 
consisting  of  nothing  but  the  'primary'  and  the  'secondary' 
coils,  the  core  and  the  terminals. 


79 


NOTES 


80 


NOTES 


81 


Electrolytic   Interrupter. 


"WEYNELT'  TYPE. 


OXYGEN        HYDROGEN 
GAS.  GAS. 


ip 


Figure  12 — (see  page  83) 


82 


CHAPTER  X. 
The  Interrupter — Tube  Shields — Valve  Tubes — Wiring  Diagrams 

It  is  necessary  in  order  to  obtain  a  practically  continuous 
current  in  the  'secondary'  coil  to  have  some  means  for  auto- 
matically 'making'  and  'breaking'  the  current  in  the  'primary.' 
We  cannot  do  this  with  sufficient  rapidity  by  means  of  the 
hand,  so  we  have  to  utilize  some  automatic  principle.  The 
instrument,  by  means  of  which  we  obtain  these  interruptions,  is 
called  an  'interrupter.* 

There  are  two  classes  of  interrupters,  mechanical  and 
electrolytic.  There  are  a  great  many  forms  of  mechanical 
interrupters,  the  simplest  of  which  is  the  ordinary  vibrator  that 
we  see  on  most  of  the  small  medical  coils  and  buzzer  bells. 
Their  operation  all  depend  upon  some  mechanical  principle,  and 
as  there  are  so  many  of  them  we  have  not  the  space  to  consider 
the  subject  in  detail.  We  will  pass  on,  therefore,  to  the  descrip- 
tion of  the  electrolytic  interrupter. 

There  are  several  forms  of  electrolytic  interrupters, 
although  they  all  depend  on  nearly  the  same  principle.  We 
will  describe,  therefore,  the  'Weynelt'  type  of  electrolytic 
interrupters.  The  construction  is  as  follows :  We  have  a 
large  battery  jar  L  (Figure  12),  which  is  nearly  filled  with  a 
solution  of  sulphuric  acid  and  water;  one  part  of  sulphuric 
acid  to  six  parts  of  water.  The  purpose  of  the  acid  in  this 
solution  is  only  to  make  the  water  a  better  conductor;  water  in 
itself  is  not  a  good  conductor  of  electricity,  but  when  it  is 
acidulated  the  conducting  power  is  very  much  increased.  Into 
this  acid  solution  we  introduce  two  electrodes,  a  positive  and 
a  negative.  The  positive  has  a  large  extent  of  surface,  while 
the  negative  has  a  very  small  extent  of  surface.  These  are 
the  two  principal  features  of  the  apparatus.     The  one  shown  in 

83 


the  illustration  G  represents  the  positive  electrode  as  a  loop 
of  lead  wire.  The  reason  why  we  use  the  metal  lead  is 
because  it  will  not  be  affected  by  the  dilute  sulphuric  acid. 

The  negative  electrode  EFI  is  more  complicated.  It  con- 
sists first  of  the  insulated  portion  E,  which  is  a  tube  of  hard 
rubber  of  vulcanite,  from  which  projects  a  small  porcelain 
tube  F.  Through  this  porcelain  tube  and  hard  rubber  tube  we 
pass  a  lead  wire  P  with  a  platinum  point  I,  the  tip  of  which 
only  extends  below  the  porcelain  tube.  This  is  the  only  part 
of  the  negative  electrode  that  is  exposed  to  the  action  of  the 
electrical  current.  By  means  of  the  set  screw  AC,  at  the  top, 
we  can  raise  or  lower  our  lead  wire  with  the  platinum  tip,  so 
that  a  greater  or  smaller  amount  of  the  platinum  extends  below 
the  porcelain  tube. 

When  we  pass  a  current  of  electricity  through  a  liquid  that 
has  two  electrodes  immersed  in  it,  we  have  the  phenomenon  of 
electrolysis  taking  place.  The  water  of  the  solution  is  decom- 
posed into  its  hydrogen  and  oxygen  elements.  Hydrogen  gas, 
therefore,  is  formed  all  over  the  surface  of  the  positive  elec- 
trode, but  these  bubbles  of  gas,  H,  do  not  remain  upon  the 
positive  electrode;  they  take  the  path  of  the  current  through 
the  liquid  and  are  deposited  upon  the  negative  electrode  I.  The 
oxygen  bubbles,  O,"  are  formed  on  the  surface  of  the  negative 
and  remain  there  because  they  cannot  flow  against  the  action 
of  the  current,  the  result  of  which  is  that  we  have  an  accumu- 
lation of  the  two  gases,  hydrogen  and  oxygen,  at  the  negative 
electrode.  In  the  case  of  the  Weynelt  Interrupter  the  positive 
electrode  has  a  great  extent  of  surface,  while  the  negative 
electrode  is  confined  to  a  very  small  platinum  tip,  which  pro- 
jects below  the  porcelain  tube,  and  the  bubbles  of  hydrogen, 
which  were  formed  all  over  the  surface  of  the  positive  elec- 
trode, passed  through  the  solution  and  were  deposited  around 
the  tip  of  the  platinum  point,  therefore  mixing  with  the  oxygen 
gas,  in  the  proportions  of  two  parts  of  hydrogen  to  one  of 
oxygen.  This  film  of  gas  completely  surrounds  the  exposed  tip 
of  the  negative  electrode,  and  acts  as  a  non-conductor  to  the 

84 


current.  Since  two  things  cannot  occupy  the  same  space  at  the 
same  time,  the  solution  and  the  gas  cannot  both  be  in  contact 
with  the  negative  point  at  the  same  instant.  Therefore,  when 
the  gas  is  in  contact  the  Hquid  is  not;  but  the  Hquid  was  the 
conductor  of  the  current;  therefore,  if  the  liquid  is  not  in 
contact  there  is  no  current  flowing.  The  circuit  of  the  current 
is  broken.  An  electrical  current  passing  from  a  large  extent 
of  surface  to  a  small  extent  of  surface  will  generate  heat  by 
resistance.  The  tip  of  the  negative  electrode  becomes  so  hot 
that  it  glows  with  a  white  heat,  therefore,  we  construct  the  tip 
of  that  electrode  of  platinum,  which  metal  has  a  high  fusing 
point.  The  mixture  of  hydrogen  and  oxygen  gases  form  an 
explosive  compound.  The  heat  developed  in  the  negative  elec- 
trode is  sufficiently  great  to  ignite  this  explosive  mixture,  and 
we  have  an  explosion.  The  chemical  result  of  the  explosion  is 
the  formation  of  water,  which  once  more  mixes  with  the 
solution,  which  again  comes  in  contact  with  the  electrode.  The 
current  is  once  more  established,  causing  the  'make'  of  the 
circuit.  Immediately  the  bubbles  will  again  form,  producing 
another  'break,'  followed  in  quick  succession  by  the  explosion 
which  again  'makes'  the  current,  and  so  on,  with  great  rapidity. 

With  the  Weynelt  Interrupter  it  is  possible  to  obtain 
250  breaks  per  second,  and  this  rate  of  interruption  may  be 
varied  by  the  turning  of  the  set  screw  at  the  top,  which  adjusts 
the  amount  of  platinum  point  extending  beyond  the  porcelain 
tube  into  the  solution.  The  greater  the  quantity  of  platinum 
exposed,  the  longer  it  will  take  for  the  bubbles  to  form,  and  the 
longer  it  will  take  for  the  surface  to  become  heated;  therefore, 
the  less  frequent  the  interruptions.  When  we  draw  up  the 
platinum  point  and  allow  a  smaller  extent  to  protrude,  we 
increase  the  rate  of  interruptions.  Almost  all  electrolytic  inter- 
rupters are  constructed  on  similar  lines  and  depend  practically 
on  the  same  explanation  for  their  operation. 

We  have  seen  from  this  description  how  we  obtain  our 
make  and  break.  Let  us  now  consider  how  we  get  our  increase 
of  potential  at  the  instant  of  the  break,  that  we  discussed  under 

85 


the  theory  of  the  induction  coil.  Let  us  go  back  to  our  old 
simile  of  the  tank  of  water  on  the  roof.  Suppose  we  have  a 
pipe  discharging  water  into  the  tank.  We  will  also  assume 
that  we  have  another  pipe  leading  out  from  the  tank  which  has 
exactly  the  same  diameter  of  opening.  You  will  see,  of  course, 
that  the  water  will  remain  a  constant  height  in  the  tank.  It 
flows  out  just  as  rapidly  as  it  flows  in.  We  will  also  place  a 
stopcock  on  the  lower  pipe,  or  the  one  leading  out  from  the 
tank.  If  we  gradually  turn  this  stopcock  closed,  what  will 
result?  The  height  of  the  water  will  rise  in  the  tank,  and  the 
amount  of  water  coming  out  will  decrease,  but  the  potential, 
or  the  strength  of  that  current,  will  increase.  What  have  we 
done?  We  have  raised  the  head  of  pressure  (analogous  to 
voltage)  and  we  have  decreased  the  rate  of  flow  (analogous 
to  amperage).  At  the  instant  that  the  stopcock  closes  off  the 
supply  of  water  the  pressure  has  reached  its  maximum  potential. 
This  principle  is  exactly  what  takes  place  in  the  interrupter.  A 
bubble  of  gas  forms  on  the  platinum  point;  then  another 
bubble;  then  another,  and  so  on,  one  after  another,  each  one 
reducing  the  surface  of  the  electrode  that  is  exposed  to  the 
action  of  the  electrical  current,  just  as  though  we  were  turning 
the  stopcock  closed  in  the  tank.  We  finally  reach  a  point  where 
all  the  bubbles  have  formed  that  can  cover  the  surface  of  the 
electrode,  with  the  exception  of  the  last  one,  which  will  close 
the  circuit.  The  potential  has  increased  bubble  by  bubble  to 
this  point  as  its  maximum.  As  the  last  bubble  forms  which 
breaks  the  current,  the  potential  of  the  current  coming  from 
the  positive  has  reached  its  maximum.  The  'break'  and  the 
maximum  'increase  of  potential'  taking  place  at  the  same 
identical  instant. 

We  have  described  three  of  the  four  essential  parts  of  the 
apparatus,  namely,  the  X  Ray  tube,  the  Induction  Coil  and  the 
Interrupter.  The  fourth  is  the  X  Ray  Tube  Shield.  This  last 
piece  of  apparatus  is  absolutely  essential,  not  to  the  working  of 
the  apparatus,  but  to  the  protection  of  the  operator.  There  are 
different  means  of  protection.     Some  operators  prefer  to  cover 

86 


their  own  persons  with  a  substance  that  is  opaque  to  the  X  Ray, 
as,  for  example,  a  suit  of  lead  armor,  thus  protecting  their 
body  from  exposure  to  the  X  Rays.  This  method  is  not  a  good 
one.  You  will  readily  appreciate  the  discomfort  of  the  operator 
carrying  about  with  him  a  heavy  suit  of  lead,  and  you  may  rest 
assured  that  the  instant  that  he  is  through  with  the  taking  of  a 
picture  and  has  turned  his  current  off,  he  will  immediately  strip 
himself  of  his  lead  suit.  He  forgets  that  the  secondary  rays, 
that  are  given  off  by  every  object  in  the  room  that  has  absorbed 
the  primary  rays,  are  still  active  in  the  room,"^  and  he  therefore 
submits  himself  to  the  secondary  radiation,  which  in  time  may 
produce  even  more  serious  results  than  those  of  the  primary 
radiations.  Another  method  that  is  sometimes  employed  for 
the  protection  of  the  operator,  is  a  large  screen  which  is  lined 
on  one  side  with  sheet  lead  or  other  substance,  opaque  to  the 
X  Ray.  This  screen  having  a  window  made  of  lead-glass  at 
about  the  height  of  the  operator's  eyes.  When  his  apparatus 
is  in  action  he  goes  behind  the  screen,  and  observes  the  working 
of  the  tube  by  watching  it  through  the  lead-glass  window. 
Again,  when  he  turns  off  the  current,  he  steps  out  boldly  from 
behind  the  screen  and  walks  up  the  tube,  forgetting  again  the 
secondary  rays.  For  dental  work  this  method  of  protection,  as 
well  as  the  first,  are  not  only  inadequate,  but  they  are  really 
dangerous  to  use.  The  best  method  of  protection  is  not  the 
shielding  of  the  patient  or  the  operator  directly,  but  to  place  a 
box  lined  with  some  material  opaque  to  the  X  Ray,  such  as  a 
lead-glass  shield  around  the  tube  itself,  thereby  confining  all 
rays,  both  primary  and  secondary,  to  the  inside  of  this  box  or 
shield.  This  device  is  called  a  Tube  Shield.  They  are  made 
in  many  different  forms,  but  their  requisite  is  that  they  be 
absolutely  opaque  to  the  X  Ray,  and  that  they  do  not  conduct 
an  electrical  current.  You  will  see,  therefore,  that  it  is  impos- 
sible to  line  this  box  with  metallic  lead,  which  would  otherwise 
be  the  best  substance  that  we  could  obtain,  for  the  reason  that 


*  The    author    has    made    an    actual    radiograph    with    the    secondary    emanations 
from  objects  in  the  laboratory  that  have  received  direct  X    Ray  exposure. 

87 


the  electrical  current  instead  of  passing  through  the  tube,  which 
has  a  high  resistance,  would,  in  preference,  jump  to  the  metallic 
lead  lining  and  would  pass  through  that  as  the  path  of  least 
resistance.  There  are  several  substances  that  have  been  used 
with  more  or  less  success  in  the  linings  of  these  shields,  all  of 
which  are  non-conductors  of  electricity.  One  of  the  best  mix- 
tures is  that  of  red  oxide  of  lead,  subnitrate  of  bismuth,  a 
little  glue  and  plaster  of  paris.  This  mixture,  when  soft,  is 
laid  in  a  layer  of  about  a  quarter  of  an  inch  thick  all  over  the 
insides  of  the  box  and  after  it  has  set  and  hardened,  is  painted 
with  a  lead  paint.  The  opacity  of  this  substance  for  the  X  Ray 
is  very  great.  There  are  other  forms,  such  as  rubber  that  has 
been  impregnated  with  lead  salts,  that  also  serve  as  good  protec- 
tion, but  it  is  decidedly  necessary  for  the  operator  before  he 
starts  work  to  secure  for  himself  a  shield  that  gives  really  good 
protection.  An  excellent  shield  is  constructed  of  glass 
impregnated  with  lead  salts,  not  affecting  its  transparency,  but 
rendering  it  proof  to  all  X  Rays,  except  those  more  penetrating 
ones  obtained  from  very  high  vacuum  tubes.  These  rays,  how- 
ever, have  hardly  any  dermatological  effects.  The  opacity  may 
be  tested  by  the  placing  of  a  film  and  an  interposed  coin,  on  the 
outside  of  the  shield  and  operating  the  tube  for  a  short  time 
and  then  developing  your  film,  thereby  determining  whether  it 
received  any  exposure  to  the  X  Ray  or  not.  If  the  shield  is  not 
safe  a  shadow  of  the  coin  will  be  seen  on  the  negative.  Of 
course  the  shield  must  have  an  opening  through  which  the  rays 
can  escape  and  reach  the  patient.  Tube  shields  are  usually 
made  with  different  size  openings.  If  constructed  of  a  material 
opaque  to  ordinary  light,  it  is  well  to  have  a  window  of  lead- 
glass,  so  that  the  working  of  the  tube  and  its  coloration  may 
be  observed  by  the  operator.  If  one  stands  out  of  the  path 
of  the  ray  as  it  emerges  from  the  opening  in  a  really  good 
shield,  he  is  absolutely  safe  from  all  exposure  to  the  ray,  and 
when  the  current  is  turned  off  he  may  rest  assured  that  what- 
ever ray  was  given  off  was  confined  to  the  tube  shield,  except 
the   small    amount   that   passed   through   the   opening,   most   of 


which  was  absorbed  by  the  patient  and  carried  away  to  be 
given  off  later  as  secondary  radiation  outside  his  office. 

When  an  induction  coil  is  used  to  generate  the  high 
potential  current,  the  'secondary'  output  is  necessarily  an  alter- 
nating current,  since  the  impulses  of  'make'  and  'break'  are  in 
opposite  directions.  As  we  use  only  the  stronger  'break'  cur- 
rent in  the  X  Ray  tube,  the  weaker  current  of  'make'  must  be 
cut  out  of  the  tube  circuit.  This  can  only  be  done  by  introduc- 
ing sufficient  resistance  in  the  'secondary'  circuit  to  prevent  the 
weaker  current  of  'make'  from  passing,  but  allowing  the 
stronger  'break'  current  to  complete  its  circuit. 

In  a  low  potential  circuit  we  would  use  a  resistance  coil 
or  rheostat  to  attain  this  result,  but  currents  of  high  voltage 
cannot  be  controlled  by  wire  resistances ;  therefore  we  must 
resort  to  the  use  of  vacuum  and  air  gaps  to  sufficiently  check 
the  high  potential  impulses  of  'make.' 

The  best  method  for  preventing  the  'make'  current  from 
passing  through  the  X  Ray  tube  is  to  employ  another  or 
auxiliary  vacuum  tube  in  the  'secondary'  circuit.  This  tube 
is  called  a  valve  tube.  It  is  constructed  on  the  same  principles 
as  the  main  X  Ray  tube,  but  has  a  funnel-shaped  anode  made 
of  aluminum,  instead  of  the  platinum  disk  of  45  degrees.  This 
anode  reflects  the  bi-ultra  violet  rays  directly  back  upon  the 
approaching  rays,  thus  retarding  them  and  reducing  their  force 
of  impact  against  the  anode.  As  the  bi-ultra  violet  rays  do  not 
impinge  upon  the  anode  with  as  great  a  force  as  they  do  in  the 
X  Ray  tube,  they  are  not  transformed  into  tri-ultra  violet.  No 
X  Rays  being  formed,  therefore,  in  the  valve  tube,  it  is  not 
necessary  to  inclose  this  tube  in  a  shield.  The  vacuum  of  these 
tubes  is  lower  than  in  the  main  tubes. 

Air  gaps,  called  spark-gaps,  are  also  employed  in  some 
circuits  to  further  cut  off  the  'make'  current  from  passing 
through  the  tube.  They  are  often  made  adjustable.  This 
objectionable  current  of  'make'  in  the  X  Ray  tube  is  frequently 
referred  to  as  "inverse  current." 

89 


AN    INDUCTION    COIL    INSTALLATION 


SECONDARY  CIRCUIT. 

VALVE  TUBE. 


PRIMARY  CIRCUIT. 


Figure  13 — (see  page  91) 


90 


Figure  13  represents  a  complete  wiring  diagram  for  an 
induction  coil  installation.  We  will  first  trace  out  the  path  of 
the  'primary'  current  indicated  by  the  straight  arrows.  It 
comes  from  the  'cutout'  on  the  commercial  circuit  supply  wires 
as  a  direct  current  of  110  volts,  and  we  will  say  about  30 
amperes.  It  enters  the  interrupter  by  its  positive  electrode  of 
lead  wire,  passes  through  this,  and  flows  through  the  primary 
coil  of  the  induction  coil  as  an  interrupted  current.  In  the 
diagram  the  'primary'  coil  is  represented  by  the  short-waved 
line,  P,  shown  as  situated  outside  of  the  'secondary.'  It  must 
be  borne  in  mind  that  this  is  only  a  diagrammatic  method  of 
representing  it.  In  reality,  the  'primary'  has  two  or  more 
windings  and  fits  snugly  inside  of  the  'secondary.'  From  the 
'primary'  coil  the  current  flows  through  a  rheostat,  R,  and  the 
switch,  B,  and  so  back  to  the  negative  side  of  the  service 
'cutout.' 

It  is  not  absolutely  necessary  to  include  a  rheostat,  or 
adjustable  'resistance  box'  in  the  'primary'  circuit.  We  do  not 
find  that  there  is  much  necessity  for  the  reducing  of  the 
primary  potential  in  dental  radiography,  other  than  when  regu- 
lating the  vacuum  of  the  tube.  Therefore,  in  some  of  the  best 
outfits  for  dental  work,  there  is  in  place  of  the  adjustable 
rheostat,  a  fixed  resistance  coil  which  can  be  introduced  into 
the  circuit  by  a  special  switch. 

The  switch,  B,  is  to  turn  on  and  off  the  primary  circuit 
in  making  the  exposure.  This  switch,  the  rheostat  or  fixed 
resistance  coil,  the  primary  coil,  and  the  interrupter,  are  all  in 
series  with  each  other,  consequently  it  makes  no  difference  as 
to  their  relative  arrangement.  The  grouping  of  them,  as  shown 
in  the  diagram,  is  purely  arbitrary. 

In  the  'secondary'  circuit  we  will  start  with  the  current  of 
'break,'  which  is  indicated  by  the  broken  arrows.  It  leaves 
the  negative  side  of  the  coil,  and  jumps  across  the  adjustable 
spark-gap,  if  open,  thence  to  the  cathode  terminal  of  the  main 
tube.  It  passes  through  the  tube,  leaving  by  the  anode,  enters 
the  anode  of  the  valve  tube,  passes  through  this,  out  through 

91 


the  cathode  of  the  valve  tube,  across  the  second  spark-gap,  and 
so  back  to  the  coil  terminal  on  the  positive  side. 

The  'make'  current,  if  it  could  flow,  would  start  out  from 
the  positive  terminal  of  the  coil,  as  represented  in  the  diagram 
by  the  wavy  arrows,  would  jump  the  spark-gap  and  enter  the 
valve  tube  by  the  cathode  terminal.  Passing  through  this 
vacuum,  it  would  enter  the  main  tube  and  flow  as  far  as  the 
surface  of  the  anode.  Here  it  would  meet  with  the  second 
vacuum  gap  that  must  be  overcome.  The  potential,  being  lower 
than  that  of  the  'break'  current,  is  not  sufficient  to  break  down 
this  added  resistance;  consequently  it  should  not  flow  at  all. 
In  practice,  however,  some  'make'  or  'inverse'  tube-current  does 
complete  the  entire  circuit,  even  the  second  spark-gap.  The 
small  amount,  however,  that  does  pass  the  resistances  can  do 
but  little  harm  in  the  actual  working  of  the  tube  and  the 
resulting  picture.  The  lower  the  vacuums  of  the  two  tubes  the 
more  apt  the  'make'  current  is  to  pass. 


92 


NOTES 


93 


NOTES 


94 


CHAPTER  XL 
The  Film  and  Its  Preparation 

Radiographs  of  the  various  parts  of  the  body  are  made 
with  especially  prepared  photographic  plates,  called  ''X  Ray 
plates."  In  dental  work,  however,  it  becomes  necessary  to 
take  pictures  inside  the  oral  cavity.  Glass  plates  are  not 
suitable  for  this  class  of  work.  We  therefore  employ  small 
cut  films  that  have  been  especially  prepared  for  the  purpose. 
These  can  be  placed  in  the  mouth  and  made  to  conform  with 
the  curvature  of  the  palate. 

The  basis  of  these  films  is  celluloid  in  thin  transparent 
sheets.  The  celluloid  backing  is  then  coated  with  an  emulsion 
of  gelatin,  that  has  been  sensitized  with  certain  chemicals, 
principally  the  silver  bromides.  This  renders  the  film  sensitive 
to  all  actinic  rays,  and,  of  course,  the  operation  of  sensitizing 
must  be  carried  on  under  the  non-actinic  light  of  a  red  lamp. 
The  exact  formula  with  which  the  films  are  sensitized  remains 
a  trade  secret  of  the  manufacturers.  There  have  been  many 
different  makes  of  films  advocated  for  dental  radiography. 
Some  are  more  rapid  than  others,  but  where  the  speed  of  the 
film  is  materially  increased,  the  contrast  or  gradations  in 
'lights  and  shadows'  will  not  be  so  good.  An  ideal  film,  espe- 
cially prepared  for  dental  radiography,  consists  of  the  'Eastman 
Dental  X  Ray  Film.'  This  film  has  been  used  with  entire 
satisfaction  by  the  author  for  the  last  ten  years.  It  is  not  a 
particularly  rapid  film,  requiring  fairly  long  exposures,  but 
where  the  element  of  time  is  not  essential;  that  is,  where  the 
type  of  apparatus  is  powerful  enough  to  give  good  results  in 
five  to  ten  seconds'  exposure,  with  these  slower  emulsion  films, 
their  use  is  certainly  to  be  advocated.  Recently  the  Eastman 
Company  have  been  experimenting  with  several  new  emulsions, 

95 


to  the  end  that  they  might  increase  the  working  speed.  They 
have  succeeded  in  turning  out  a  film  about  five  times  as  fast 
as  their  old  ones.  After  repeated  trials  with  the  new  films  the 
author  has  gone  back  to  the  old  ones,  getting  better  grades  of 
contrast  with  the  slower  emulsion.  Another  film  that  is  used 
extensively  is  an  English  product,  made  by  the  Ilford  Company 
of  London.  These  films  are  made  in  several  sizes  and  shapes. 
They  are,  by  actual  test,  about  ten  times  as  fast  as  the  'old' 
Eastman  film.  Where  great  speed  is  required,  as,  for  example, 
with  some  of  the  types  of  apparatus  that  give  but  a  minimum 
potential,  their  use  is  to  be  strongly  recommended. 

The  standard  size  of  the  dental  film  is  1%  x  1^  inches. 
This  is  a  good  average  size,  and  can  conveniently  be  placed  in 
the  mouth.  In  cases  of  very  small  children,  the  size  may  be 
cut  down  by  the  operator. 

The  'old'  Eastman  film  is  supplied  in  small  paper  packets 
of  standard  size.  There  are  two  films  placed  in  each  packet,  so 
that  two  duplicate  radiographs  are  made  by  the  single  exposure. 
This  is  a  most  useful  and  desirable  practice.  The  films  are 
wrapped  in  black  paper  when  received ;  each  packet  being 
sealed  by  a  white  paster  on  the  back,  or  non-sensitive  film 
surface  of  the  packet.  The  films  are  lightproof  when  received, 
but  they  are  not  moistureproof.  They  cannot  be  placed  in  the 
mouth  as  they  are,  as  the  saliva  would  penetrate  the  black 
paper  and  ruin  the  films  inside.  We  must  prepare  these  films 
before  using,  by  wrapping  them  in  thin  sheets  of  palate  rubber 
or  other  moistureproof  material.  The  author  uses  an  extra 
thin  grade  of  palate  rubber,  made  in  two  colors — the  brown  or 
pure  rubber  and  red.  The  paper  packets  are  laid  sensitive  side 
dozvn,  upon  the  red  rubber,  the  cloth  covering  being  first 
stripped  off  one  side  of  the  rubber.  A  sheet  of  the  pure  rubber 
is  then  placed  over  the  packet  and  allowed  to  overlap  a  little, 
the  same  as  with  the  red.  On  pressing  the  edges  tightly 
together,  by  running  an  instrument  of  some  kind,  or  the  finger 
nail,  around  the  outline  of  the  film  packet,  the  two  rubber 
surfaces    will    cohere   perfectly.      The    surplus    rubber    is    then 

96 


trimmed  off,  care  being  taken  not  to  cut  into  the  paper  packet. 
The  resulting  packet  is  quite  waterproof. 

Films  should  not,  however,  be  wrapped  in  rubber  for  any 
length  of  time,  as  the  sulphur  in  the  rubber  will  work  its  way 
through  the  paper  film  covering  and  injure  the  films.  It  is 
not  well  to  leave  films  so  prepared  longer  than  about  twelve 
hours  in  the  rubber  covering.  The  'new'  Eastman  film  is 
furnished  in  an  outer  covering  of  red  waxed  paper.  This  is 
moistureproof  in  itself  and  needs  no  extra  rubber  wrapping. 
The  Ilford  films  are  wrapped  in  an  outer  coating  of  gutta- 
percha, which  protects  them  from  moisture. 

Some  makes  of  dental  films  have  rounded  corners,  so  that 
when  placed  in  the  mouth  the  corners  will  not  dig  into  the 
tissues. 

As  a  matter  of  fact,  the  number  of  cases  where  the  sharp 
cornered  film  causes  any  real  discomfort  to  the  patient  are 
very  few,  and  the  operator  can,  in  those  cases,  go  into  his 
dark  room,  and  with  the  light  of  his  red  lamp  trim  away  the 
one  offending  corner,  and  rewrap  the  film.  This  is  a  better 
practice  than  rounding  all  the  corners  of  all  films,  since  we  do 
not  sacrifice  any  of  the  valuable  film  surface,  which  is  really 
small  enough  as  it  is. 


97 


NOTES 


98 


CHAPTER  XII. 
Application  of  the  Principles  of  Shadows,  to  Avoid  Distortion 

Before  proceeding  with  the  methods  of  placing  the  film  in 
the  mouth,  we  will  first  take  up  a  few  principles  that  have 
an  important  bearing  on  this  part  of  the  subject. 

''A  dental  radiograph  might  be  defined  as  a  shadowgraphic 
representation  of  the  several  dental  tissues,  taken  plane  by 
plane,  and  each  plane  superimposed  on  the  next,  from  facial 
to  lingual  surface/'  Note  particularly  that  the  radiograph  is  a 
'shadowgraphic'  and  not  a  'photographic'  representation  of  the 
tissues.  The  images  that  we  see  on  a  dental  negative  are  not 
the  actual  teeth  photographed  on  the  film,  but  merely  shadows 
of  the  actual  teeth.  Since,  therefore,  we  deal  only  with 
shadows,  you  will  readily  appreciate  how  easily  these  shadows 
may  be  distorted.  Wherever  a  shadow  is  cast,  it  must  be  of 
some  object  that  is  between  the  surface  upon  which  the  shadow 
is  thrown,  and  a  source  of  illumination.  The  source  of  illu- 
mination may  be  the  sun,  an  arc  lamp,  or  other  light-producing 
medium,  or  it  may  be  the  radiations  from  an  X  Ray  tube.  The 
surface  upon  which  the  shadow  is  cast  we  will  call  the  'screen.' 
The  relative  positions  of  the  object,  the  source  of  illumination, 
and  the  screen,  determine  the  size  of  the  resulting  shadow. 
Shadows  may  be  distorted  by  'elongation'  or  by  'foreshortening.' 
The  same  laws  apply  to  the  shadows  cast  by  the  X  Ray,  as 
with  any  other  source  of  illumination. 

The  closer  the  object  is  to  the  screen  the  clearer  and 
sharper  will  be  the  resulting  shadow,  and  the  more  exact  in 
size.  Hold  your  hand  between  a  lamp  and  a  sheet  of  white 
paper,  as  a  screen,  at  the  distance  of  about  a  foot  from  it, 
and  observe  the  shadow  cast. 

99 


SHADOWS 


Foce-sKortening       0^     Shadows. 


\"' 


Fig.  14 


Fig.  15. 


Fig.  16. 


Elongation     Oj     SKadows. i 


Fig.l7 


100 


You  will  note  first  that  it  is  very  much  enlarged,  and 
secondly,  the  outline  will  be  faint  and  indistinct.  Now  slowly 
approach  the  screen  with  your  hand.  You  will  observe  that 
the  shadow  becomes  more  distinct  and  smaller,  till  at  length, 
when  the  hand  is  almost  touching  the  screen,  the  shadow  will 
be  good  and  black,  and  of  almost  the  exact  size  of  the  actual 
hand.  From  this  experiment,  we  learn  that  in  radiography  the 
closer  we  get  the  plate  or  film  to  the  tissues  we  wish  to  show, 
the  clearer  and  sharper  will  the  resulting  picture  be. 

Let  us  refer  to  Figure  14,  which  represents  a  man  standing 
on  a  sidewalk  at  night,  with  an  arc  lamp  directly  over  his  head. 
The  arc  lamp  is  represented  by  A.  The  direction  of  the  rays 
of  light  by  AD,  and  the  shadow  of  the  man  cast  upon  the  walk 
as  BC.  When  the  source  of  light  is  directly  over  the  man  the 
only  shadow  that  is  thrown  at  all  is  a  small  spot  directly  at 
his  feet.  Now  suppose  that  the  man  takes  a  step  forward  and 
assumes  the  relative  position  with  the  arc  lamp  as  shown  in 
Figure  15.  His  shadow  begins  to  take  shape,  but  it  is  con- 
siderably shorter  than  the  actual  height  of  the  man.  If  he 
now  takes  another  step  forward,  as  shown  in  Figure  16,  the 
shadow  will  assume  its  correct  length;  that  is,  equal  to  the 
height  of  the  man.  Once  more,  suppose  the  man  took  another 
step  forward,  till  the  relative  positions  of  the  man  and  the  lamp 
are  as  shown  in  Figure  17.  The  shadow  is  now  much  longer 
than  the  height  of  the  man.  It  is  an  elongated  shadow.  If  he 
were  to  continue  to  advance,  the  shadow  would  also  continue 
to  elongate,  till,  at  length,  when  the  lamp  was  directly  behind 
the  man  the  length  of  the  shadow  would  be  'infinity.'  We 
see,  therefore,  that,  as  the  relative  positions  of  the  object  and 
the  source  of  illumination  vary,  so  the  length  of  the  resulting 
shadow  upon  the  screen    varies  from  nothing  to   infinity. 

In  the  dental  radiograph  the  shadows  of  the  teeth  upon 
the  film  would  also  vary  from  nothing  to  infinity,  according  as 
we  changed  the  position  of  the  X  Ray  tube.  We  must  be  able 
to  determine  just  where  to  place  the  tube  in  order  to  get  a 
resulting  shadowgraph   of   the   teeth   with   correct   root-lengths. 

101 


Let  us  again  refer  to  Figure  16 — the  plane  of  the  object  will 
be  represented  by  the  line  EDB,  and  the  screen  by  the  line  BC. 
These  two  lines  form,  with  each  other,  the  angle  EBC,  which 
in  this  case  is  a  right  angle.  If  we  bisect  this  angle  we  get 
the  line  FHB,  and  we  note  that  the  direction  of  the  rays 
indicated  by  the  line  AHC  is  perpendicular  to  the  bisecting 
plane  at  the  point  H.  When  this  takes  place  the  resulting 
shadow  will  be  the  same  length  as  the  object. 

From  the  above  illustration  we  may  formulate  a  rule  for 
the  directing  of  the  rays  of  light  to  fall  upon  a  given  object,  so 
as  to  get  a  correct  shadow  length  upon  a  screen  placed  at  an 
angle  to  the  object.  This  rule  may  be  expressed  as  follows : 
'Bisect  the  angle  made  by  the  plane  of  the  object,  and  the  plane 
of  the  screen,  and  direct  the  rays  so  that  they  will  fall  per- 
pendicular to  this  bisecting  plane.' 

Let  us  see  how  this  rule  works  out  as  applied  to  the 
taking  of  a  radiograph  of  the  teeth.  Figure  18  represents  a 
sectional  diagram  of  a  superior  right  bicuspid  tooth  situated  in 
its  socket  in  the  alveolar  process  of  the  superior  maxilla.  T  is 
the  tooth,  S  represents  the  antrum  or  maxillary  sinus,  and 
D  the  film  placed  in  the  mouth  and  pressed  up  into  the 
curvature  of  the  palate.  The  line  AB  represents  the  plane  of 
the  teeth,  and  CB  the  mean  or  average  plane  of  the  curved 
film.  Suppose  we  place  the  X  Ray  tube  at  X,  and  direct  the 
rays,  as  shown  by  the  arrow,  perpendicular  to  the  plane  of  the 
tooth.  Will  we  get  a  correct  shadow  length  of  the  roots  of 
the  tooth  upon  the  film?  We  will  plot  out  the  projection  of 
the  tooth  upon  the  film  and  see.  Draw  two  lines  from  the 
tube  X  to  either  end  of  the  film,  as  XY  and  XF.  These  lines 
intersect  the  tooth  at  M  and  N,  therefore  a  shadow  of  that  part 
of  the  tooth  between  the  points  M  and  N  will  be  projected 
upon  the  film  D,  and  will  have  the  length  of  the  dotted  line 
EF.  This  line  is  much  longer  than  the  line  AIX,  consequently 
we  have,  in  this  case,  considerable  elongation.  The  apex  of 
the  root  will  not  be  shown  at  all  upon  the  film,  since,  if  we 
draw  a  line   from  the  tube  X  to  the  apex  of  the  tooth's  root 

102 


x->c-rr.' 


Elongation 

X  ^  Fig.18 


CoTrect  Shadow  Len^lK 


rig.20.      B 

(See  pages  102  and  104) 


103 


and  continue  it  to  Z,  we  see  that  it  does  not  touch  the  film 
at  all. 

From  this  diagram  we  learn  that  in  the  superior  arch  we 
cannot  direct  the  rays  perpendicular  to  the  plane  of  the  teeth. 

Referring  now  to  Figure  19,  we  will  direct  the  rays  per- 
pendicular to  the  mean  plane  of  the  film.  In  this  case  the 
projected  shadow  of  the  tooth  EF  is  shorter  than  the  actual 
tooth  length,  therefore  we  see  that  by  directing  the  rays  per- 
pendicular to  the  mean  plane  of  the  teeth  we  get  foreshortening 
in  the  root  lengths.  We  note,  however,  that  in  this  diagram  the 
line  XY,  representing  the  extreme  upper  limit  of  the  field  of  the 
picture,  passes  through  the  antrum,  and  gives  us  a  shadow  of 
its  lower  half. 

In  Figure  20  the  line  KB  represents  a  plane  bisecting  the 
angle  made  by  the  plane  of  the  teeth,  AB,  and  the  mean  plane 
of  the  film,  CB.  If  we  direct  the  rays  perpendicular  to  this 
bisecting  plane,  and  at  a  point  opposite  the  apices  of  the  roots 
of  the  teeth,  the  resulting  radiograph  will  give  us  approximately 
correct  root-lengths,  as  shown  by  comparing  the  lengths  of  the 
lines  EF  and  MN.  Note  carefully  the  relative  positions  of  the 
X  Ray  tube,  and  the  film,  to  obtain  this  result.  Of  course  the 
position  of  the  tube,  as  regards  the  exterior  part  of  the  face 
of  the  patient,  will  vary  according  as  the  patient  has  a  high 
or  a  low  palate. 

Suppose  we  had  to  obtain  a  radiograph  of  the  maxillary 
sinus,  we  would  raise  the  tube  up  still  higher  than  as  shown  in 
Figure  19,  and  direct  the  rays  downward,  in  a  line  just  passing 
under  the  patient's  eye.  Of  course  the  film  should  be  placed 
higher  across  the  palate,  in  which  case  only  the  apices  of  the 
roots  of  the  teeth  will  show  on  the  lower  part  of  the  negative. 


104 


NOTES 


105 


NOTES 


106 


4 
« 


CHAPTER  XIIL 
Technique  of  Taking  the  Picture 

Before  taking  a  dental  radiograph  the  operator  should 
ascertain,  whenever  possible,  the  'suspected'  condition  of  the 
patient  that  renders  the  radiograph  desirable.  Of  course 
this  is  not  always  evident,  but  there  are  times  when 
we  wish  to  inspect  a  certain  root-canal  as  to  the  extent  that  it 
has  been  filled,  for  example,  or  again,  we  may  be  looking  for 
the  presence  and  position  of  an  unerupted  tooth.  In  the  first 
case  we  should  take  the  picture  so  that  the  resulting  shadows 
would  be  of  the  correct  length.  In  the  second  case  the  actual 
root-lengths  are  not  at  all  necessary  to  show ;  in  fact,  we  should 
purposely  foreshorten  the  shadows  on  the  radiograph,  so  as  to 
cover  the  area  above  the  roots  of  the  teeth,  where  the  missing 
tooth  is  most  likely  to  be.  We  should  always  endeavor  to  so 
direct  the  rays  as  to  show  with  the  maximum  clearness  the  area 
that  we  believe  to  be  involved.  From  this  you  will  see  that 
we  do  not,  in  every  case,  try  for  correct  shadow  lengths,  but 
in  many  cases — in  fact,  we  may  say  the  majority  of  cases — we 
deliberately  distort  the  shadow  lengths  for  the  purpose  of 
covering  a  higher  area.  The  only  distortion,  however,  that  we 
consider  permissible  is  that  of  foreshortening.  Under  no  con- 
ditions do  we  elongate  the  shadows.  Pictures  showing  any  such 
distortion  are  evidence  of  faulty  technique.  Foreshortening  the 
shadows  does  not  render  them  any  the  less  clear,  as  does  elonga- 
tion, but  rather  it  tends  to  intensify  the  detail.  In  cases  where 
we  deliberately  foreshorten  the  shadows  we  take  this  fact  into 
consideration   in  the  subsequent  translation  of  the   radiograph. 

Let  us  suppose  that  we  are  thoroughly  equipped  for  the 
taking  of  dental  radiographs,  with  an  up-to-date  outfit,  we  will 
say,  a  coil  installation,  and  a  patient  presents  with  a  history  of 

107 


a  fistulous  tract  in  the  region  of  the  superior  right  bicuspids, 
discharging  pus  into  the  mouth.  We  presume  that  there  is  an 
abscess  somewhere,  we  might  attempt  to  locate  it  without 
resorting  to  the  X  Ray,  but  we  would  only  be  wasting  the 
patient's  time  and  our  own  as  well.  We  turn,  therefore,  to  a 
radiograph.  Let  us  follow,  step  by  step,  the  procedure  in  the 
taking  of  this  radiograph. 

We  first  see  that  the  patient  is  comfortably  seated  in  the 
dental  chair,  or  some  other  chair  with  a  good  head-rest.  The 
head  should  be  so  adjusted  that  it  is  almost  erect  and  securely 
placed  in  the  head  rest.  We  then  proceed  to  the  preparation 
of  the  film.  Films  and  plates  should  be  always  kept  in  a  lead- 
lined,  X  Ray  proof  box,  or  else  in  a  room  far  removed  from 
the  operating  room,  otherwise  they  might  be  prematurely 
exposed,  if  the  tube  shield  should  be  pointed  in  their  direction. 
We  take  a  film,  therefore,  from  our  lead-lined  box  and  wrap  it 
in  palate  rubber,  unless  it  is  one  that  has  been  already  made 
waterproof.  We  are  careful  in  wrapping  it  that  we  get  the 
sensitive  side  of  the  film  package  against  the  red  rubber.  The 
film  is  then  placed  back  in  the  box. 

We  next  examine  carefully  the  patient's  mouth  and  note 
whether  the  palate  is  high  or  low.  If  we  are  not  experienced 
in  the  taking  of  these  pictures  we  should  proceed  at  this  stage 
with  deliberation  and  special  care.  We  consider  the  area  we 
wish  to  show.  As  it  is  a  suspected  abscess  condition  the 
direction  in  which  it  points  is  unknown.  The  antrum  even 
may  be  involved.  We  wish  to  show  as  much  of  the  area 
above  the  teeth  as  we  can  without  sacrificing  the  roots 
themselves. 

We  must,  accordingly,  foreshorten  the  shadows  somewhat. 
We  come  to  the  conclusion  that  if  we  place  the  tube  so  that 
the  rays  are  directed  perpendicularly  to  the  plane  of  the  film 
we  will  include  considerable  area  above  the  roots  of  the 
teeth,  and  will  show  even  the  floor  of  the  antrum.  (See 
Figure  19.)  It  is  not  as  easy  to  direct  the  rays  perpendicular 
to   a  given  plane  in  practice  as   it  is  to  plot  it  out  on  paper. 

108 


However,  with  a  little  practice,  this  will  come  by  instinct.  The 
experienced  operator  subconsciously  places  the  tube  in  the  posi- 
tion to  best  show  the  condition,  depending  on  the  height  of  the 
patient's  palate.  For  this  reason  it  is  well,  from  the  start,  to 
note  very  carefully  this  height  in  each  case,  and  to  associate 
it  in  your  mind  with  the  position  in  which  you  place  your  tube. 
For  the  beginner,  it  is  well  to  actually  plot  out  on  the  patient's 
face  imaginary  lines  that  coincide  with  the  planes  of  the  teeth 
and  the  film,  and  even  the  bisecting  plane. 

In  nearly  every  case  certain  'landmarks'  will  present  which 
will  serve  as  guides  to  these  imaginary  lines.  For  example, 
with  the  case  we  have  assumed,  let  us  suppose  that  the  mean 
plane  of  the  film  in  the  mouth  coincides  with  an  imaginary  line 
drawn  on  the  patient's  face  from  the  right-hand  corner  of  the 
mouth  to  the  inner  corner  of  the  left  eye.  JVith  this  imaginary 
line  in  mind,  move  your  tube  shield  till  the  direction  of  the 
rays,  as  they  will  come  through  the  opening,  will  fall  perpen- 
dicular to  a  plane  passing  through  the  face  along  the  imaginary 
line. 

When  you  have  the  tube  shield  adjusted  to  the  proper 
angle  caution  your  patient  not  to  move  the  head  under  any 
consideration,  and  then  connect  the  wires  to  your  tube  shield. 
Be  particular  to  see  that  the  wire  connected  to  the  valve  tube 
side  of  the  coil  leads  to  the  anode  of  the  main  tube.  When 
this  is  done  tell  your  patient  that  you  are  going  to  turn  on 
the  current,  and  that  there  may  be  a  slight  noise  of  sparking,  but 
not  to  'jump'  or  change  the  position  of  the  head.  Now  close 
the  switch  of  your  'primary'  circuit  and  allow  the  current  to 
pass  for  about  two  or  three  seconds  only.  Note  whether  the 
current  is  passing  through  the  tube  in  the  right  direction  by 
observing  if  the  hemispheres  of  activity  and  non-activity  are 
well  marked.  Also  note  if  the  coloration  is  good,  indicating 
the  proper  degree  of  vacuum,  and  that  the  current  is  not 
jumping  to  any  nearby  object. 

If  all  appears  well  in  this  flash-view,  flash  it  again  "to 
make   assurance   doubly   sure."      Then,    still   finding   everything 

109 


all  right,  wash  your  hands  thoroughly,  procure  the  film  that  you 
have  wrapped  from  its  box  and  take  off  the  cloth  covering 
from  both  sides  of  the  palate  rubber,  bend  the  package  in 
your  fingers  several  times  to  make  it  flexible,  and  insert  the 
package  in  the  patient's  mouth,  being  careful  to  place  the  red 
or  sensitive  side  toward  the  tube.  Press  this  well  into  the 
curvature  of  the  palate,  being  particular  not  to  let  the  inside 
top  corner  come  in  contact  with  the  soft  palate  if  you  can 
possibly  avoid  it.  Now  remove  your  fingers,  first  telling  the 
patient  to  put  the  left  (in  this  case)  index  finger  on  the  film 
and  to  gently  press  it  steadily  against  the  side  of  the  roof  of 
the  mouth.  Once  more  look  to  the  position  of  your  tube  and 
see  if  in  placing  the  film  in  the  mouth  you  upset  the  proper 
angle;  if  not,  tell  your  patient  that  you  are  going  to  take  the 
picture  and  to  keep  absolutely  motionless.  If  your  type  of 
apparatus  allows  the  taking  of  the  picture  in  but  a  few  seconds 
caution  your  patient,  in  addition,  to  take  a  long  breath  and 
hold  it. 

Now,  stop-watch  in  hand,  or  at  least  a  watch  with  a 
second  hand,  close  your  switch  sharply  and  make  the  expo- 
sure, timing  it  very  carefully.  During  the  exposure  observe 
the  appearance  of  the  tube,  whether  the  vacuum  is  lowering  or 
not,  the  reading  of  your  milliamperemeter,  if  you  have  one  in 
the  secondary  circuit ;  and  above  all,  watch  your  patient,  and 
see  if  you  observe  any  movement.  If  you  do,  stop  the  exposure 
and  take  another. 

When  the  exposure  is  complete,  open  your  switch  and 
remove  the  film  from  the  patient's  mouth.  This  done,  strip  the 
rubber  from  the  film  packet,  write  its  number  on  the  back,  put 
it  in  an  envelope  with  the  name  and  other  data  on  it  and  return 
the  paper  film  packet  to  the  lead-lined  box.  Disconnect  the 
tube  and  move  the  shield  away  from  the  patient's  chair. 

The  above  procedure  should  be  followed  as  closely  as 
possible  in  every  case.  Of  course  there  will  be  circumstances 
that  will  alter  each  individual  case,  and  they  will  have  to  be 
dealt  with  accordingly. 

110 


In  radiographing  the  inferior  molars  and  bicuspids  the  film 
will  be  about  parallel  to  the  plane  of  the  teeth,  and  the  rays 
can  be  directed  perpendicular  to  it.  In  all  other  cases  you  will 
have  to  take  into  consideration  the  bisecting  plane  or  the  film 
plane.  Try,  wherever  possible,  to  get  the  upper  edge  of  the 
film  flush  with  the  morsal  surfaces  of  the  teeth  in  cases  of  the 
lower  arch. 

In  some  cases  you  may  have  trouble  getting  the  patient  to 
hold  the  film  in  the  mouth.  NBVBR,  UNDER  ANY  CIR- 
CUMSTANCES, HOLD  THE  FILM  IN  THE  MOUTH 
YOURSELF  DURING  THE  EXPOSURE!  This  caution 
cannot  be  emphasized  too  strongly.  The  temptation  is  often 
great  to  hold  the  film  in  a  difficult  case,  hut  don't  do  it! 
Your  hand,  in  holding  the  film,  receives  as  much  exposure  as 
the  patient  does,  which  in  itself  is  negligible,  but  if  you  do  it 
once  you  are  apt  to  repeat  it  with  other  cases,  and  before  you 
are  aware  of  it  you  have  exceeded  the  limit  of  safety  and  will 
develop  a  case  of  dermatitis.  The  effects  of  the  X  Ray  are 
unfortunately  accumulative,  and  an  exposure  of  ten  seconds  to- 
day, twenty  to-morrow  and  twenty  next  week,  and  even  ten 
next  month,  would  have  the  same  effect  as  one  minute  exposure 
at  one  sitting.  There  are  many  of  the  early  operators  who 
have  lost  their  fingers,  hands,  arms,  and  even  their  lives,  as 
the  result  of  exposure  years  ago,  before  the  danger  of  the  ray 
was  known.  It  is  not  so  much  the  direct  effects  (the  der- 
matitis) that  is  so  serious,  but  it  is  the  X  Ray  cancers  that 
develop  on  the  seat  of  the  old  dermatitis  years  later.  Be 
warned  in  time  and  you  will  find  that  there  is  no  more  danger 
in  radiology  as  practiced  to-day  than  in  photography  itself. 

In  cases  where  you  may  have  trouble  in  getting  the  patient 
to  hold  the  film  in  the  mouth,  you  may  be  able  to  get  someone 
who,  perhaps,  is  accompanying  the  patient,  to  do  so.  If  this  is 
impossible  there  is  always  one  method  that  we  can  use,  which 
we  will  consider  when  we  come  to  the  technique  of  stereoscopic 
dental  radiography. 

Ill 


The  distance  of  the  tube  from  the  face  makes  a  good  deal 
of  difference  in  the  time  of  exposure.  The  intensity  of  the 
X  Ray,  like  any  other  form  of  light,  varies  inversely  with  the 
square  of  the  distance  from  the  object  illuminated.  It  is  not 
well  to  have  the  tube  too  close,  because  the  shadow  will  be 
enlarged.  In  practice  18  to  24  inches  will  be  about  right. 
Whatever  distance  you  adopt,  with  your  outfit,  keep  this  dis- 
tance constant  in  all  your  pictures.  It  is  not  advisable  to  have 
too  many  variable  factors  in  your  technique.  The  more  constant 
we  keep  the  conditions  under  which  we  work  the  better  will 
be  our  results. 

The  four  most  difficult  radiographs  to  get  in  the  mouth 
are  the  four  third  molars.  The  superior  third  molars,  and 
even  the  second  and  first,  are  hard  to  get,  because  the  inside 
top  corner  of  the  film  packet  is  apt  to  come  in  contact  with 
the  soft  palate  and  cause  the  patient  to  gag.  When  the  patient 
once  starts  to  gag  there  is  little  hope  of  getting  the  picture 
without  anaesthetizing  the  palate.  In  placing  the  film  in  the 
mouth,  in  a  superior  molar  case,  be  very  careful  not  to  push 
it  too  far  back.  In  fact,  it  is  better  to  place  it  in  about  the 
bicuspid  region,  and  very  slowly  and  carefully  work  it  back 
till,  at  length,  we  get  it  far  enough  back  to  show  the  third 
molar  area  without  having  touched  the  soft  palate  at  all.  x\lso 
be  careful  in  putting  the  film  in,  that  the  inside  edge  does  not 
drop  down  and  touch  the  back  part  of  the  tongue.  If  patients 
show  any  tendency  to  gag,  caution  them  to  take  several  long 
and  deep  breaths  through  the  nose.  If,  in  spite  of  these  pre- 
cautions, they  commence  to  gag,  and  they  often  will,  there  is 
only  one  thing  to  do,  and  that  is  to  anaesthetize  the  palate. 
This  is  done  by  using  a  5%  solution  (3%  with  children)  of 
cocaine,  and  to  spray  it  on  the  hard  and  soft  palates  with  an 
atomizer.  They  should  be  told  not  to  swallow  any  more  of  the 
solution  than  they  can  possibly  help.  In  about  five  minutes 
after  this  operation  you  can  proceed  to  the  taking  of  the  picture 
without  any  more  trouble. 

112 


The  inferior  third  molars  are  hard  to  get  in  many  cases, 
because  the  corner  of  the  film  is  apt  to  dig  into  the  floor  of 
the  mouth  under  the  tongue.  The  film  should  not  be  cut  if 
you  can  possibly  avoid  doing  so.  In  these  cases  we  should 
remove  the  packet  from  the  mouth,  and  taking  the  two  rubber 
surfaces  over  the  offending  corner,  between  the  thumb  and 
forefinger  of  the  right  hand,  and  holding  the  rest  of  the  packet 
securely  with  the  other  hand,  pull  out  the  rubber  a  little  at  the 
corner  and  then  pat  it  back  again.  This  should  make  a  little 
pad  or  cushion  over  the  sharp  point  of  the  film.  Another 
method  is  to  bend  the  corner  back  and  so  give  it  a  rounded 
effect.  Either  of  these  methods  is  usually  sufficient,  but  there 
are  some  cases,  with  a  very  small  mouth,  where  it  is  absolutely 
necessary  to  cut  off  the  corner.  This,  of  course,  must  be  done 
in  the  dark  room  with  the  aid  of  the  red  lamp.  The  black 
rubber  can  then  be  pulled  down  over  the  cut  and  lapped  over. 
However,  if  this  is  done  the  rubber  must  not  be  removed  till 
you  are  ready  to  develop  it  in  the  dark  room.  And  that  should 
be  as  soon  as  possible  after  taking.  Also  the  packet  should 
not  be  exposed  to  any  bright  light,  but  should  be  shielded  as 
much  as  possible  by  the  hand.  The  safer  method,  though,  if 
you  have  the  time,  is  to  unwrap  the  film  in  the  dark  room,  cut 
the  corner  of  the  film  itself,  rewrap  it  in  its  black  paper, 
turning  over  the  corner  of  the  paper  where  you  have  snipped 
off  the  film,  and  then  rewrap  the  packet  in  palate  rubber. 

In  taking  pictures  of  the  inferior  teeth  always  try  to  get 
the  film  down  low  enough  to  show  the  lower  border  of  the 
inferior  maxilla.  This  is  not  always  possible,  but  if  you  proceed 
gently,  but  slowly  and  firmly,  watching  carefully  for  the 
wincing  of  the  patient,  you  will  be  surprised  in  many  cases 
how  far  down  you  are  able  to  press  the  film. 

In  pictures  of  the  inferior  centrals  the  patient's  head  should 
be  dropped  very  far  back  in  the  head  rest,  and  the  tube  shield 
placed  over  the  chest.  The  rays  should  then  be  directed  per- 
pendicular to  the  plane  of  the  fihn. 

113 


Before  leaving  the  subject  of  the  technique  of  taking  the 
picture,  we  will  summarize  the  steps  that  should  always  be 
observed.  It  would  be  well  for  the  beginner  to  commit  this 
procedure  to  memory,  rather  than  to  hesitate  in  the  presence 
of  the  patient.  There  is  nothing  so  disquieting  and  less  reassur- 
ing to  the  patient  than  signs  of  indecision  on  the  part  of  the 
operator. 

In  the  taking  of  a  dental  radiograph  always  proceed  as 
follows : 

FIRST.     GET  THE  PATIENT  COMFORTABLE. 

SECOND.  PREPARE  THE  FILM  IF  YOU  HAVE 
NOT  ALREADY  DONE  SO. 

THIRD.  EXAMINE  CAREFULLY  THE  PATIENT'S 
MOUTH. 

FOURTH.  ADJUST  THE  TUBE  SHIELD  TO 
DIRECT  THE  RAY  PROPERLY. 

FIFTH.  CAUTION  THE  PATIENT  NOT  TO  MOVE 
THE  HEAD. 

SIXTH.  CONNECT  UP  YOUR  TUBE  AND  FLASH 
IT  TWICE. 

SEVENTH.     WASH  YOUR  HANDS  THOROUGHLY. 

EIGHTH.  INSERT  THE  FILM  PACKET  IN  THE 
MOUTH. 

NINTH.  REMOVE  YOUR  FINGERS,  AND  LET  THE 
PATIENT  HOLD  THE  FILM. 

TENTH.  READJUST  YOUR  TUBE-SHIELD  IF 
NECESSARY. 

ELEVENTH.  AGAIN  CAUTION  YOUR  PATIENT 
TO  KEEP  ABSOLUTELY  STILL. 

TWELFTH.  TURN  ON  THE  CURRENT  AND  MAKE 
THE  EXPOSURE. 

114 


THIRTEENTH.  REMOVE  THE  FILM  FROM  THE 
MOUTH,  AND  WASH  YOUR  HANDS  AND  THE  RUB- 
BER PACKET. 

FOURTEENTH.  DISCONNECT  THE  WIRES  AND 
MOVE  AWAY  THE  SHIELD. 

FIFTEENTH.  STRIP  OFF  THE  RUBBER  COVER- 
ING FROM  THE  FILM  PACKET. 

SIXTEENTH.  WRITE  NUMBER  AND  NAME  ON 
FILM  PACKET. 

SEVENTEENTH.  PUT  FILM  PACKET  IN 
ENVELOPE. 

EIGHTEENTH.  PUT  ENVELOPE  IN  LEAD  BOX 
TILL  READY  TO  DEVELOP. 

Learn  these   eighteen   steps   carefully  and   always   observe 

them  as  far  as  possible.  The  author  has  found,  by  the  expe- 
rience  of  many  years,   that  these   steps   are   all   necessary   and 

should  be  adhered  to  in  their  right  order  if  satisfactory  work 
is  to  be  accomplished. 

Particularly  in  clinic  work  should  these  directions  be 
insisted  on. 


115 


NOTES 


116 


NOTES 


117 


FILM    CLAMP 


Figure  21 — (see  page  111)) 


118 


CHAPTER  XIV. 
Development  and  Mounting  of  Negatives 

The  development  of  X  Ray  films  is  carried  out  very  much 
the  same  as  with  ordinary  photographs.  The  operator  who  has 
had  any  experience  with  amateur  developing  should  find  this 
the  easiest  part  of  the  subject. 

The  first  requisite  is  a  dark  room.  This  can  be  a  closet 
that  has  been  fitted  with  a  table  or  wide  shelf,  about  three 
or  four  feet  from  the  floor,  and  preferably  electric  light  for  the 
dark-room  lamp.  Red  lamps  may  be  purchased  from  any  photo- 
graphic supply  store  to  burn  either  electricity,  oil  or  candles. 
Running  water  is  also  desirable  in  the  dark  room,  but  it  is  not 
essential,  providing  you  can  use  it  in  another  room.  Dental 
films  should  not  be  developed  in  photographic  trays,  but 
tumblers  or  small  glass  troughs  should  be  used.  Three  of  these 
should  be  provided.  The  author  has  found  that  the  rectangular 
trough-covers  of  butter  dishes,  that  may  be  bought  in  the  nearest 
10-cent  store,  answer  admirably,  the  bottoms  of  which  can  be 
used  for  covers.  The  films  are  hung  in  these  dishes,  or  where 
only  two  or  three  negatives  are  to  be  developed  at  a  time, 
ordinary  tumblers  will  answer  perfectly.  Throughout  the  entire 
operation  of  developing,  fixing,  washing  and  drying,  the  films 
are  held  in  small  clamps  that  were  devised  by  the  author  many 
years  ago.  They  may  be  obtained  from  the  American  X  Ray 
Equipment  Co.,  of  New  York.  The  accompanying  illustration 
shows  how  the  film  is  held  in  the  clamp  (Figure  21).  Small 
tags  are  attached  to  each  clamp,  on  which  is  written  the  serial 
number  of  the  radiograph,  or  even  the  patient's  name.  In 
this  way  the  negatives  are  never  mixed  up  while  developing 
several  at  one  time.     The  operator  should  have  at  least  a  dozen 

119 


Rubij  Lamp. 


Water. 


FixinoBatK.  Developer 


Figure  22 — (see  page  121) 


120 


of  these  clamps  on  hand,  and  if  he  expects  to  do  much  work 
several  dozen  will  be  found  very  desirable. 

The  developer  Used  in  dental  work  is  far  more  concen- 
trated than  the  ordinary  photographic  developers.  The  formula 
that  is  best  to  use  will  be  found  in  the  package  in  which  the 
dental  films  are  bought.  Different  manufacturers  of  dental  film 
advocate  different  formulae  for  development.  The  formula  for 
the  fixing  bath  is  also  given  in  the  direction  sheets  that  accom- 
pany all  makes  of  films. 

The  technique  for  developing  is  as  follows :  We  will 
suppose  that  we  have  taken  two  radiographs  and  are  ready 
to  develop  them.  We  go  into  the  dark  room  and  before  shut- 
ting out  the  white  light  prepare  the  solutions  and  film  clamps. 
We  take  three  glass  troughs  that  have  been  well  washed,  and 
fill  one  of  them  with  water  and  place  it  as  shown  in  Figure  22. 
Fill  another  with  the  developing  solution  and  place  it  on  the 
right,  while  the  third  is  filled  with  the  fixing  bath  and  placed 
on  the  left,  as  shown  in  the  diagram.  A  towel  is  also  provided 
and  placed  alongside  the  troughs  on  the  shelf  or  table. 

Four  clamps  are  now  tagged  and  the  number  of  the  first 
film  is  written  on  two  of  them,  while  the  number  of  the 
second  film  is  written  on  the  other  two.  Each  pair  of  clamps, 
with  its  corresponding  film  packet,  are  placed  on  the  shelf 
some  distance  apart,  so  that  no  mistake  can  be  made  in  the 
dark,  and  the  wrong  films  placed  in  the  clamps.  When 
everything  is  ready,  light  the  red  lamp  and  put  out  any  other 
white  light  and  close  the  door  of  the  dark  room.  Take  one 
of  the  film  packets  and  open  it.  Take  only  one  of  the  films 
out,  holding  the  other  wrapped  in  the  black  paper  in  your 
hand  and  place  the  film  in  the  clamp.  Be  sure  to  get  the 
sensitive  or  dull  side  out,  or  away  from  the  clamp.  The  dull 
side  can  be  readily  distinguished  from  the  shiny  side,  by  holding 
the  film  in  front  of  the  red  lamp  and  catching  the  reflection  of 
the  light  on  its  surface.     The  dullest  reflection  is  the  sensitive 

side. 

121 


FILM  MOUNTS 


M. 


CASE  NO. 
DATE 


(VIEW   ONLY   BY   STRONG   TRANSMITTED   UGHT.) 


UNGUAL    ASPECT 


TELEPHONE 
STU  YVES  ANT    1500 


Dr.  F.  L.  R.  SATTERLEE,  Jr. 

148  EAST  18Ui  ST..  N«w  York  City 


M. 


CASE  NO. 
DATE 


(VIEW    ONLY    BY    STRONG    TRANSMITTED    LIGHT.) 


UNGUAL    ASPECT 


TELEPHONE 
STU  YVES  ANT    1500 


Dr.  F.  L.  R.  SATTERLEE.  Jr. 

148  EAST  18th  ST..  New  York  Cky 


■iiPiiiiiii^^ 


mm^ 


Figure  23 — (see  page  123) 
122 


When  the  first  film  is  in  the  clamp,  hang  it  in  the  glass 
trough  containing  water.  Now  take  the  other  film  from  the 
packet  you  are  holding  in  your  hand  and  place  that  in  the  other 
clamp.  Hang  this  also  in  the  water.  Take  the  first  film  and 
clamp  and  move  it  up  and  down  a  few  times,  to  be  sure  that 
the  surface  is  thoroughly  wet  and  that  no  air  bubbles  adhere 
to  it.  Place  it  in  the  developing  solution  on  the  right.  Do  the 
same  with  the  second  film. 

Observe  that  the  film  is  whitish  and  translucent  by  trans- 
mitted light,  when  first  placed  in  the  developer.  Take  the  films 
out  from  time  to  time  and  hold  them  up  to  the  red  lamp  for  a 
few  seconds  at  a  time  only.  Watch  the  image  appear  on  these 
first  pictures  by  occasional  inspection.  The  films  are  kept  in 
the  developing  bath  until,  on  looking  through  the  film  at  the 
red  light,  the  whole  film  looks  quite  black,  and  no  detail  is 
discernible.  Then  remove  the  films  from  the  developer,  and 
rinsing  them  by  dipping  them  a  few  times  in  the  water,  transfer 
them  to  the  fixing  bath.  You  can  now  proceed  with  the  other 
two  films  in  the  second  packet.  Until  you  are  thoroughly 
familiar  with  the  developing  operation,  it  is  not  well  to  open  a 
second  packet  till  you  have  the  first  films  in  the  fixing  bath. 
The  films  are  left  in  the  fixing  bath  until  they  have  cleared  as 
much  as  they  will,  about  ten  minutes.  They  are  then  taken 
out  and  hung  back  in  the  water  bath.  After  all  the  films  are 
*fixed,'  that  is,  made  non-sensitive  to  actinic  rays,  the  white 
light  may  be  admitted  to  the  room. 

The  films  are  now  hung  in  another  large  vessel,  such  as  a 
battery  jar,  or  a  deep  tray,  and  this  is  placed  under  a  tap  of 
running  cold  water  for  about  twenty  minutes  or  longer.  They 
may  then  be  hung  in  an  empty  battery  jar  to  dry,  first  swabbing 
them  off  very  lightly  with  a  small  piece  of  wet  absorbent  cotton. 
Care  must  be  taken  not  to  dislodge  the  film  from  its  clamp  in 
this  operation.  Do  not  fail  to  immerse  the  films  in  water, 
before  and  after,  both  the  developing  and  fixing  baths. 

When  the  films  are  thoroughly  dry  they  are  then  ready 
for    mounting.      Figure    23     represents    a    mount    devised    by 

123 


the  author  for  dental  negatives.  These  mounts  consist  of 
rectangles  of  celluloid,  4^^  x  2^  inches.  The  celluloid  being 
clear  on  one  side  and  dull  on  the  other,  resembling  ground 
glass.  In  the  center  a  rectangular  border  is  printed  the  size  of 
the  dental  picture  and  slits  are  punched  in  the  corners  of  this 
to  take  the  corresponding  corners  of  the  film.  The  film  is 
slipped  into  these  mounts  film  side  down. 

On  these  mounts  are  printed  the  necessary  blanks  to  be 
filled  in  for  the  recording  of  the  patient's  name,  the  case  number 
and  date.  At  the  bottom  of  the  mount  appears  your  own  name 
and  address.  Just  below  the  printed  rectangle  appear  the 
words,  "Lingual  Aspect,"  and  directly  above  the  directions, 
"View  only  by  strong  transmitted  light." 

These  cards  can  be  filed  in  an  index  and  serve  as  an 
admirable  method  for  the  preserving  of  the  pictures  properly 
filled  in  with  the  necessary  data.  When  a  negative  is  examined 
by  holding  it  up  to  a  strong  light  the  dull  surface  of  the 
celluloid  gives  a  fine  backing  and  prevents  the  seeing  of  objects 
through  it,  such  as  the  filament  in  an  electric  lamp  used  to 
view  it  with.  Such  objects  tend  to  obliterate  the  detail  in  the 
picture  and  confuse  the  operator* 


*  These    mounts    may    be    purchased    from    the    Swenarton     Stationery    Co.,    of 
New  York,  printed  to  order  with  your  name,  etc. 


124 


NOTES 


125 


Figure  24 — (see  page  127) 


126 


CHAPTER  XV. 

Head  Pictures  on  Plates 

There  are  cases  that  arise  in  dental  radiography  where  we 
cannot  get  the  picture  on  a  film  in  the  mouth.  For  example, 
we  may  have  a  patient  present  with  a  fracture  of  the  inferior 
maxilla.  The  jaws  may  be  completely  or  even  partially 
ankylosed,  and  consequently  it  will  be  impossible  to  get  a  film 
in  the  mouth.  Again  we  may  have  to  obtain  a  radiograph  of 
the  ramus  or  even  the  condyle.  In  these  cases  we  must  take 
the  radiograph  on  a  glass  plate. 

There  are  two  very  good  X  Ray  plates  on  the  market,  the 
'Wrattan  and  Wainwright,'  made  by  the  Eastman  Co.  of 
Rochester,  New  York,  and  the  'Ilford'  plate,  made  by  the 
Ilford  Co.  of  London. 

These  plates  can  be  obtained  in  both  6 J/2  x  8}4,  and 
8  X  10  sizes,  the  only  sizes  that  we  would  use.  They  are 
wrapped  in  two  thicknesses  of  envelopes,  the  first  black  and 
the  second  or  outside  one  orange  colored.  This  renders  them 
lightproof. 

The  patient  is  seated  sideways  in  the  chair,  with  the  head 
thrown  away  back  and  the  involved  inferior  maxilla  pressed 
against  the  head  rest  The  plate  is  then  slipped  between  the 
head  and  the  head  rest,  the  pressure  of  the  head  against  it 
being  sufficient  to  keep  it  in  place.  The  tube  shield  is  so  placed 
as  to  direct  the  rays  from  the  opposite  side,  pointing  slightly 
upward,  so  that  the  shadow  of  the  maxilla  on  the  opposite  side 
just  escapes  being  superimposed  on  the  affected  side.  It  will 
require  some  little  practice  to  get  the  right  angle  every  time. 
The  accompanying  diagram,  Figure  24,  shows  approximately 
the  relative  positions  of  the  head,  the  plate  and  the  head  rest, 
and  the  direction  of  the  rays. 

127 


These  plates  are  developed  in  trays  the  same  as  any  other 
photographic  plates,  only  using  the  developing  and  fixing  baths 
the  manufacturers  recommend  in  the  printed  slip  that  accom- 
panies every  box  of  plates. 

Radiographs  should  not  be  made  on  plates  if  we  can 
possibly  show  the  required  area  on  a  film  in  the  mouth.  The 
tissues  are  further  from  the  'screen,'  resulting,  therefore,  in  a 
sacrifice  of  clearness  and  detail.  Also,  we  are  prone  to  get 
superimposition  of  the  tissues  of  the  opposite  side.  Many 
hospitals  and  radiologists  not  familiar  with  the  special  dental 
technique  attempt  to  take  all  dental  conditions  on  plates.  This 
practice  results  in  the  prejudice  that  many  dentists  have  against 
the  resort  to  radiography  in  doubtful  cases.  They  have,  unfor- 
tunately, only  had  experience  with  plates  that  have  been  made 
for  them  by  general  radiologists  without  the  knowledge  of  the 
special  dental  technique,  and  the  finer  detail  that  would  have 
been  of  great  assistance  was  entirely  lost.  Radiographs  on 
plates  of  conditions  of  the  superior  maxilla  are  particularly 
unsatisfactory. 

Prints  of  both  plate  and  film  negatives  are  rarely  made 
to-day,  the  dentist  preferring  to  make  his  diagnosis  from  the 
negative  directly.  Printing  is  a  purely  mechanical  process  and 
consequently  there  must  be  some  loss  in  the  transfer.  The 
original  negative  has  more  detail  than  can  be  obtained  in  any 
print.  All  reproductions  of  radiographs  in  this  book  are 
negative  reproductions,  just  as  though  the  actual  negative  were 
before  you  (but  there  is  considerable  loss  of  detail  due  to  the 
reproduction).  This  is  done  so  that  the  student  may  become 
accustomed  to  the  X  Ray  negative  appearance  of  radiographs. 
In  the  negative  dense  objects  appear  white,  while  the  converse 
is  true  with  prints.  Plate  negatives  may  be  marked  with  the 
operator's  name  and  its  serial  number  at  the  time  of  exposure. 
Small  plates  of  aluminum  are  stamped  with  the  name,  and  the 
letters  filled  in  with  red  lead.  Numbers  are  placed  on  the 
markers  in  the  same  manner.  These  name  plates,  or  markers, 
are  placed  on  the  X  Ray  plate  and  are  left  there  during  the 

128 


exposure,  so  that,  on  development,  a  radiograph  is  also  made 
of  the  marker  which  leaves  only  the  shadow  of  the  letters 
and  numbers. 


129 


NOTES 


130 


CHAPTER  XVI. 
Dangers  of  the  X  Ray 

Shortly  after  the  discovery  of  the  X  Ray,  it  became  known 
that  many  who  were  exposed  to  the  rays  developed  a  condition 
of  the  superficial  tissues  resembling  in  appearance  that  of 
sunburn.  For  some  time  these  effects  were  not  traced  to  the 
ray  itself,  but  were  thought  to  have  been  produced  by  the  high 
potential  discharge.  This  theory  was,  however,  soon  proved 
to  be  wrong,  and  it  was  found  that  the  rays  themselves  were 
to  blame.  Experimenters  then  became  more  careful  about 
exposing  themselves  to  this  powerful  agent,  that  could  produce 
these  "burns"  as  they  began  to  be  called.  Next  came  the  reports 
of  more  effects  of  these  wonderful  rays,  such  as  the  falling 
out  of  the  hair,  pigmentation  of  the  skin,  and  the  cracking  or 
splitting  of  the  finger  nails.  In  fact,  in  several  cases  severe 
'burns'  were  reported  and  the  complete  loss  of  the  finger  nails. 
These  'burns'  were  very  hard  to  heal,  resisting  all  means  of 
treatment.  For  awhile  these  alarming  reports  threatened  to 
entirely  discourage  the  investigators.  It  was  then  found  that 
these  rays,  that  had  the  power  to  produce  such  changes  in  the 
healthy  tissues,  could  also  be  used  to  advantage  in  the  treat- 
ment of  certain  pathological  conditions  of  the  skin.  Interest 
was  again  aroused,  and  means  were  devised  by  which  operators 
could  work  around  these  rays  with  comparative  safety. 

Since  that  time,  now  many  years  ago,  the  entire  subject 
has  been  studied,  analyzed  and  developed,  until  to-day  we  are 
no  longer  working  in  the  dark  with  an  unknown  agent,  more 
dangerous  in  its  effects  than  even  opium  and  morphine. 

The  effects  of  the  X  Ray  may  to-day  be  classed  under  two 
main  divisions,  primary  and  secondary.  The  primary  effects 
are  due  to  direct  exposure  to  the  rays  themselves  for  a  period 

131 


of  time  sufficient  to  produce  certain  changes  in  the  skin  known 
as  Rontgen  Dermatitis.  This  dermatitis  may  be  of  five  degrees. 
The  first  degree  resembles  a  slight  sunburn  in  appearance. 
There  is  a  slight  pinkish  erythema,  dry  in  character,  and  with- 
out destruction  of  tissue.  There  may  be  some  sensation  of 
burning  or  tingling  such  as  accompanies  sunburn.  In  second 
degree  dermatitis  there  is,  in  addition,  the  presence  of  vesicles 
and  the  surface  becomes  moist  or  weeping.  The  sensations  at 
this  stage  resemble  those  of  a  blistering  burn  of  any  character. 
If  all  exposure  to  the  rays  is  stopped  at  this  point,  the  result 
will  probably  be  a  slow  cleaning  up  of  the  condition  and  a 
slight  desquamation,  and  perhaps  a  permanent  pigmentation. 
Third  degree  dermatitis  is  characterized  by  an  angry  red 
appearance  with  intense  congestion,  which  is  moist  and  weeping 
all  the  time.  Upon  the  raw  and  sometimes  bleeding  surface 
there  forms  a  yellowish-white  necrotic  membrane.  This  mem- 
brane, however,  is  made  up  of  only  epithelium.  The  connective 
tissue  beneath  is  not  affected,  except  for  more  or  less  swelling. 
If  all  X  Ray  exposures  were  now  stopped  the  condition  would 
gradually  but  slowly  subside,  and  in  the  course  of  two  or  three 
months  the  ruptured  vesicles  and  suppurating  necrotic  mem- 
brane would  dry  up,  and  would,  in  turn,  be  followed  by  a 
horny  epidermis  that  would  appear  in  spots  over  the  affected 
area.  Many  cases  are  considerably  retarded  by  the  reappearance 
of  the  vesicles,  and  the  repetition  of  this  process  of  throwing  off 
and  building  up  sometimes  keeps  up  for  months  and  even 
years.  In  time,  however,  the  relapses  cease,  and  the  permanent 
horny  epidermis  spreads  over  the  entire  area.  This  new  skin 
is  quite  smooth  and  natural  looking,  except  for  the  absence  of 
all  hairs  and  follicles.  For  some  time  the  new  coating  of  the 
epidermis  is  quite  sensitive  to  external  irritations. 

Dermatitis  of  the  fourth  degree  is  characterized  by  a  still 
greater  erythema  and  the  degree  of  congestion  is  much  more 
intense;  in  fact,  the  outer  coating  of  the  skin  becomes  mummi- 
fied, in  places  surrounding  actual  ulcerations  of  the  lower 
connective    tissue.      There    are    great    masses    of    dead    tissue 

132 


which,  if  not  removed  surgically,  will  result  in  gangrene. 
Patients  suffering  from  this  degree  of  dermatitis  usually  com- 
plain of  great  pain.  In  time,  if  all  exposure  to  the  X  Ray 
ceases,  even  this  advanced  condition  of  necrotic  destruction 
will  clear  up,  but  it  may  take  years  for  the  reconstruction  to 
take  place.  In  the  end  the  new  skin  is  hard  and  horny  and 
covered  in  places  by  scar  tissue. 

The  fifth  degree  of  Rontgen  Dermatitis  may  be  called 
"chronic"  dermatitis.  It  takes  place  principally  on  the  hands  of 
operators,  and  other  workers  around  the  ray,  who  may  be 
exposed,  from  time  to  time,  over  a  long  period.  They  are 
continually  adding  to  the  effects  without  getting  entirely  well 
of  the  old.  The  skin  becomes  thin  and  atrophic  with  red 
patches  of  a  vascular  nature.  There  is  an  entire  absence  of 
all  follicles  and  hair.  Codman,  in  the  Philadelphia  Medical 
Journal  (1902),  describes  this  condition  as  follows:  "In  the 
less  pronounced  forms  the  skin  appears  chapped  and  roughened 
and  the  normal  markings  are  destroyed ;  at  the  knuckles  the 
folds  of  the  skin  are  swollen  and  stiff,  while  between  there  is  a 
peculiar  dotting  resembling  small  capillary  hemorrhages.  The 
nutrition  of  the  nails  is  affected  so  that  the  longitudinal  stria- 
tions  become  marked  and  the  substance  becomes  brittle.  If 
the  process  is  more  severe  there  is  a  formation  of  blebs, 
exfoliation  of  epidermis  and  loss  of  the  nails.  In  the  worst 
form  the  skin  is  entirely  destroyed  in  places,  the  nails  do  not 
reappear  and  the  tendons  and  joints  are  damaged." 

Other  primary  effects  are  the  loss  of  the  hair,  finger  nails, 
and  even  an  acute  toxemia  with  accompanying  fever.  This 
latter  condition  is  quite  rare  and  only  develops  where  there  is 
a  marked  idiosyncrasy  to  X  Ray  reaction.  In  cases  where  the 
hair  of  the  head  receives  the  exposure  from  a  low  or  even  a 
medium  vacuum  tube  the  hair  comes  out  quite  easily  from  an 
exposure  not  even  long  enough  to  produce  a  slight  erythema 
of  the  scalp.  Hair  lost  in  this  manner,  however,  comes  back 
in  about  six  weeks  with  a  fine  thick  growth,  providing  the 
exposure  was  not  long  enough  to  destroy  the  follicles. 

133 


The  secondary  effects  of  the  X  Ray  are  far  more  subtle 
in  their  action  than  the  primary,  taking  place  as  they  do 
sometimes  after  a  lapse  of  many  years  from  the  time  of  original 
exposure.  First  we  will  mention  the  development  of  deposits 
particularly  around  the  knuckles  of  the  hands  of  X  Ray 
workers.  These  horny  excrescences  finally  develop  into  hyper- 
keratosis. These  keratoses  sometimes  have  an  inflamed  base 
which,  in  time,  gives  way  to  an  epitheliomatous  degeneration. 
Epitheliomas  developed  in  this  way  show  no  improvement  as 
the  years  go  by,  and  the  operator  is  indeed  fortunate  if  they 
do  not  spread.  There  are  many  cases  of  carcinoma  that  have 
for  their  origin  the  keratosis  on  the  hands  of  X  Ray  workers. 
If  these  conditions  continue  to  spread,  the  only  way  to  check 
the  depradation  is  amputation.  These  cases,  however,  only 
occur  where  the  victim  has  repeatedly  expos-ed  himself  to  the 
X  Ray  and  has  taken  no  precautions.  Fortunately  these  cases 
will  occur  no  more,  owing  to  the  perfect  methods  of  protection 
practised  to-day.  The  operator  who  starts  to-day  to  take  up 
radiology  can  proceed  without  danger,  thanks  to  the  knowledge 
we  have  gained  from  the  unfortunate  pioneers  who  sacrificed 
themselves  unknowingly  to  the  cause  of  science. 

Another  secondary  effect  of  the  X  Rays  is  its  action  on 
all  embryonic  tissue.  This  action  tends  to  break  down  and 
destroy  the  developing  cells.  Many  years  after  the  X  Ray 
was  discovered  it  became  known  that  those  who  had  been 
subjected  to  continual  exposures  of  short  duration,  in  the  course 
of  their  work  with  the  rays,  had  become  sterile,  or  unable  to 
reproduce  their  kind.  This  was  found  to  be  caused  by  the 
destruction  of  the  spermatozoa  in  the  male  and  the  primordial 
ovules  in  the  female.  The  cells  involved  in  these  cases  were  of 
embryonic  origin.  Sterility  produced  in  this  manner  is  not 
accompanied  by  impotence.  Whether  these  cases  are  perma- 
nently affected  we  are  not  prepared  to  say.  Some  writers 
believe  that  the  condition  is  but  temporary,  and  its  effects  will 
pass  away  as  the  operator  ceases  to  further  expose  himself  to 
the   rays.      It   is   more   likely,   though,   that    if   the   amount   of 

134 


exposure  has  been  sufficient  or  prolonged  over  a  great  many 
years    that  the  condition  becomes  permanent. 

There  are  numerous  other  systemic  effects  that  are  pro- 
duced, and  they  differ  somewhat  in  individuals.  In  some  there 
is  a  tendency  to  low  body-temperature ;  as  low  as  96.3  degrees  F. 
has  been  observed  as  a  normal  temperature  of  a  pioneer 
investigator. 

The  student  reading  of  these  effects  of  the  X  Ray  should 
not  become  frightened  and  hesitate  to  use  this  wonderful 
diagnostic  agent.  He  should,  however,  fear  the  ray  and  respect 
it  to  the  extent  of  carefully  following  a  technique  of  protection 
that  insures  him  against  its  casualties.  With  the  modern 
method  of  procedure  the  protection  is  complete,  and  the  opera- 
tor should  never  be  subjected  to  any  exposure  at  all.  Because 
we  know  that  sulphuric  acid  is  a  deadly  and  caustic  liquid  we 
are  not  afraid  to  keep  it  properly  bottled  for  use.  As  long  as 
we  know  the  danger  of  the  X  Ray,  we  reduce  the  possibilities 
of  the  deleterious  effects. 

The  danger  to  the  patient  exposed  to  the  X  Ray  is  prac- 
tically nil.  Radiographs  of  all  parts  of  the  body  are  to-day 
made  with  the  improved  apparatus  in  but  a  few  seconds  at 
the  most.  This  short  exposure  is  not  sufficient  to  produce  the 
slightest  effect,  either  primary  or  secondary. 

Instruments  have  been  devised  to  measure  the  dosage  of 
the  X  Ray.  Perhaps  the  most  used  is  the  Radiometer  of 
Holznecht.  By  means  of  this  device  the  rays  emanated  from  a 
vacuum  tube  for  the  purpose  of  therapeutic  application,  or 
even  for  the  taking  of  a  radiograph,  can  be  measured  by  its 
chemical  effect  upon  a  prepared  pastil  exposed  simultaneously. 
This  chemical  pastil  changes  color  during  its  exposure  to  the 
rays  and  the  shade  of  color  is  compared  with  a  scale  devised 
by  Sabouraud. 

The  intensity  of  the  rays  is  measured  in  units  called 
Holznecht's  units,  or  as  they  are  generally  spoken  of  as  H's. 
For  example,  the  dose  necessary  to  produce  the  slightest 
erythema  on  the  face  of  an  adult  is  equivalent  to  three  of  the 

135 


Holznecht  units,  or  3H.  Now  the  greatest  dose  necessary  for 
the  taking  of  a  radiograph  is  but  a  small  fraction  of  a  single 
H  unit.  From  this  you  will  see  the  enormous  margin  of  safety 
under  which  we  are  working  in  the  exposure  of  our  patients. 
If  to-day  an  erythema  is  produced  on  a  patient,  from  the  effect 
of  the  exposure  employed  for  the  taking  of  a  radiograph,  it  is 
due  entirely  to  the  faulty  technique  of  the  operator.  There 
is  no  excuse  for  such  a  thing  happening,  even  where  there  is 
a  marked  idiosyncrasy  toward  X  Ray  effects  on  the  part  of 
the  patient. 


136 


RADIOGRAPHS 


Figure   26 — (see    page    177) 


155 


156 


157 


Figure   29 — (see   page   181) 


Figure   30 — (see   page   183) 

158 


Figure   31 — (see   page   184) 


Figure   32 — (see   page   184) 

159 


Figure   33 — (see  page  184) 


Figure   34 — (see    page    1S5) 
160 


Figure   35 — (see   page    185) 


Figure   36 — (see   page   185) 

161 


Figure  37 — (see  page   185) 


Figure   38 — (see   page   ISo) 

162 


Figure   39 — (see   page   185) 


Figure   40 — (see   page    1S5) 
163 


Figure  41  —  (see  pag-e   185) 


Figure  42 — (see   page   185) 
164 


Figure  43 — (see  page   185) 


Figure  44 — (see  page  186) 
165 


Figure  45 — (see   page   1S6) 


Figure  46 — (see  page   186) 
166 


Figure  47 — (see  page   1S6) 


Figure  48 — (see   page   1S7) 


167 


Figure  49 — (see   page   1S7) 


Figure   50 — (see   page   1S7) 


168 


Figure  51  —  (see   page   1S7) 


Figure   52 — (see  page   187) 
169 


Figure  53 — (see  page   1S7) 


Figure  54 — (see   page  1S7) 
170 


Figure  05 — (see   page  187) 


Figure   56 — (Ksee  page   187) 

171 


Figure  57 — (see  page  187) 


172 


173 


DENTAL     RADIOSCOPE 


Figure  59 — (see  page  193) 


174 


DENTAL     RADIOSCOPE   (Sectional  View) 


H 


H 


Figure  60 — (see   page  193) 


175 


CHAPTER  XVII. 
Reading  the  Negatives 

In  order  to  properly  translate  the  findings  of  a  dental 
radiograph  we  must  first  become  familiar  with  the  normal 
appearances  of  the  several  tissues  involved  in  the  dental 
anatomy,  as  shown  in  the  X  Ray  negative. 

The  dental  radiograph  we  have  defined  as  'a  shadowgraphic 
representation  of  the  tissues,  taken  in  a  series  of  planes  from 
facial  to  lingual  surface.'  We  therefore  have  to  read  the 
condition  presented  in  the  negative  by  the  shadows  they  throw, 
and  in  most  cases  to  read  through  the  superimposed  tissues. 
All  tissues  are  represented  by  a  certain  intensity  of  shadow, 
governed  by  the  corresponding  density  of  the  actual  part.  In 
the  negative  dense  tissue  is  characterized  by  white  areas,  while 
tissues  less  dense  are  shown  by  darker  appearances.  Absence 
of  tissue  is  indicated  by  black  portions  of  the  negative. 

Figure  26  represents  a  dental  radiograph  enlarged  to  twice 
the  actual  size,  and  shows  the  normal  X  Ray  appearances  of 
the  tissues.  We  will  start  with  the  lightest  area  shown,  as 
'A,'  which  represents  an  amalgam  filling  in  the  crown  of  the 
first  molar  tooth.  The  next  lighter  shade  is  seen  in  the  crowns 
of  the  teeth  themselves,  as  'B.'  Then  we  find  the  shadow 
getting  darker  as  the  density  of  the  tooth  structure  becomes 
less,  as  'C  representing  the  roots  of  the  teeth.  Next  comes 
the  thicker  portions  of  the  process  'D,'  and  then  the  white  line 
*E/  which  borders  the  sockets  of  the  roots.  This  tissue  repre- 
sents the  most  recently  developed  portion  of  the  alveolar  wall, 
and  is  made  up  of  heavier  deposits  of  lime  salts.  *F'  marks 
the  grade  of  density  shown  by  the  white  lines  that  represent 
the  divisions  between  the  interstices  of  the  alveolar  process. 
All  cancellous  bone  tissue  is  characterized  in  its  X  Ray  appear- 
ance by  this  whitish  network  structure.  The  next  gradation 
of   density  is   shown  by  the  appearance  of  the  pulp   chambers 

177 


and  canals  of  the  several  teeth  'G.'  The  pulp  itself  being 
essentially  soft  tissue  is  not  shown  in  the  radiograph,  but  the 
space  occupied  by  soft  tissue  is  outlined  by  dark  areas.  This 
is  also  illustrated  by  the  space  occupied  by  the  periosteum,  or 
peridental  membrane,  lining  the  tooth  sockets  shown  by  the 
line  'H'  surrounding  the  roots.  The  compact  bone  tissue  'K' 
is  in  this  case  shown  as  having  little  density.  This  dark 
appearance  in  the  radiograph  is  caused  by  the  very  thin  structure 
of  the  inferior  maxilla  at  this  point.  This  degree  of  density 
varies  greatly  in  individuals,  and  no  approximate  gradation  of 
shade  can  be  established  to  characterize  the  normal  appearance 
in  all  cases.  We  can  also  see  a  still  darker  line  running  through 
the  compact  bone  tissue  and  parallel  to  the  lower  border  of  the 
maxilla.  This  dark  line,  X,'  is  the  inferior  dental  canal.  The 
blackest  part  of  the  picture  is  the  area,  'M,'  which  represents 
the  complete  absence  of  tissue,  as  shown  by  the  spaces  between 
and  above  the  crowns  of  the  teeth. 

This  radiograph,  as  shown  in  Figure  26,  should  be  care- 
fully studied  and  compared  with  Figure  27,  which  represents 
a  still  greater  enlargement  from  the  same  negative.  These 
various  gradations  of  density  should  be  borne  in  mind  con- 
stantly as  representing  the  normal  X  Ray  appearances  of  the 
dental  tissues.  Now  turn  to  Figure  28  and  observe  how  these 
comparative  densities  will  appear  in  the  actual  size  radiograph 
without  enlargement.  In  practice  you  will  have  to  make  your 
diagnosis  from  this  small  normal-sized  picture;  therefore  it 
would  be  well  to  compare  it  carefully  with  the  two  enlarge- 
ments from  the  same  negative.  All  other  radiographs  illus- 
trating the  various  pathological  conditions  we  will  reproduce  as 
negatives  enlarged  to  twice  the  size,  for  the  purpose  of  amplify- 
ing the  finer  detail  that  might  be  lost  in  the  process  of  book 
reproduction.*      In   stating   that   these   enlargements    are   twice 


*  It  is  absolutely  impossible,  with  printer's  ink,  to  faithfully  reproduce  all 
the  fineness  of  detail  and  contrast  that  we  can  see  on  the  translucent  negative 
viewed  by  transmitted  light.  The  twofold  enlargement  of  the  negatives  serves  to 
bring  out,  to  a  certain  extent,  the  finer  lines  of  detail,  but  owing  to  the  additional 
process,  there  is  a  corresponding  loss  of  contrast  or  gradation  between  light  and  dark 
areas.     As  these   radiographic  negatives   are   reproduced   primarily  for   the   instruction 

178 


the  size  of  the  original  negative  it  must  be  understood  that 
each  dimension  of  the  picture  is  twice  as  large,  although  the 
actual  area  of  the  radiograph  is  fouf  times  as  great. 

The  next  important  step,  after  differentiating  between  the 
shadows  that  indicate  the  densities  of  the  several  parts  of  the 
dental  negative,  is  to  correctly  get  our  bearings  in  regard  to 
the  teeth  we  are  looking  at,  and  their  positions  relative  to  the 
part  of  the  mouth  in  which  they  are  situated.  This  is  called 
'orienting'  the  picture.  The  reproductions  in  this  book  are 
the  same  as  though  we  looked  through  the  glossy  or  non- 
sensitive  side  of  the  film,  and  represents  the  lingual  aspect  of 
the  teeth  and  surrounding  tissues  in  all  cases.  From  this  we 
will  note  that  in  the  first  radiograph  we  show,  from  left  to 
right,  the  third,  second  and  first  molars,  and  part  of  the 
second  bicuspid  of  the  inferior  left  maxilla.  Another  fact  that 
we  must  consider  in  the  translation  of  the  radiographs,  is  that 
in  some  cases  only  two  or  three  teeth  in  the  center  of  the 
picture  show  very  clearly,  while  the  others,  particularly  those 
at  the  edges  of  the  film,  are  more  or  less  indistinct.  This  is 
caused  by  the  curvature  of  the  arch  which  brings  two  or  three 
teeth  directly  in  the  field  of  the  rays,  while  the  others  are  more 
or  less  superimposed  oft  each  other,  or  else  are  distorted  by 
the  curvature  of  the  film  conforming  to  that  of  the  palate,  and 
so  destroying  the  uniformity  of  the  angle  that  the  direct  rays 
from  the  tube,  form  with  the  film. 

We  have  seen  how  the  various  gradations  of  density  of 
the  several  parts  may  be  compared  on  the  individual  radiograph, 
but  these  gradations  in  one  picture  cannot  be  compared  with 
the  relative  densities  of  another,  which  may  have  been  taken 
under  different  conditions  of  penetration  in  the  X  Ray  tube. 
A  slight  difference  in  degree  of  vacuum  in  the  tube  will  give 
marked  variations  in  the  relative  contrasts  of  two  pictures. 


of  the  student,  the  author  has  permitted,  in  a  few  cases,  a  certain  amount  of 
retouching  of  these  enlargements,  under  his  personal  supervision,  to  the  extent  only 
of  strengthening  the  contrasts  between  light  and  dark  areas,  so  that  they  may 
approach  the  actual  gradations  seen  in  the  original  negative.  In  no  case  Ms  detail 
been  inserted   or  gradations   brought  out   that  could   not   be  seen   in   the   original  film. 

179 


NOTES 


180 


CHAPTER  XVIII. 

Diagnosis  of  Pathological  Conditions 

Having  considered  the  normal  appearance  of  the  dental 
tissues  under  the  X  Ray,  we  will  now  turn  our  attention  to  the 
variations  from  the  normal  that  we  meet  with  in  the  presence 
of  pathological  conditions.  Let  us  first  consider  a  typical  case 
of  alveolar  abscess.  Where  an  abscess  takes  place  in  the 
alveolar  process,  we  always  have  an  accompanying  destruction 
of  cancellous  bone  tissue.  From  our  consideration  of  the  nor- 
mal picture  we  have  learned  that  absence  of  tissue  is  charac- 
terized on  the  radiograph  by  dark  areas.  We,  therefore,  must 
look  for  a  dark  area  in  the  case  of  an  alveolar  abscess.  Let  us 
examine  Figure  29  (Case  I.).  Here  we  see,  from  left  to 
right,  the  superior  left  first  bicuspid,  cuspid  and  lateral  incisor 
teeth.  We  note  that  the  bicuspid  is  capped,  the  gold  crown 
showing  very  white,  owing  to  its  density,  and  we  also  observe 
that  this  cap  does  not  accurately  fit  the  crown  of  the  tooth. 
Above  the  gold  cap  is  seen  a  white  line  running  upward  in  the 
root  canal  and  extending  about  two-thirds  of  the  way  to  the 
apex.  From  its  whiteness  we  judge  that  it  must  be  some  very 
dense  substance,  and  we  come  to  the  conclusion  that  it  must 
be  filling  material.  Note  particularly  that  the  apical  end  of 
the  canal  is  not  filled,  and  then  observe  the  circumscribed  dark 
area  in  the  alveolar  process  surrounding  the  apex  of  the  root. 
This  dark  area  indicates  lack  of  density  or  absence  of  tissue. 
In  this  case  the  density  of  the  process  should  be  homogeneous, 
therefore  we  are  led  to  believe  that  an  actual  cavity  (to  account 
for  the  absence  of  tissue)  must  exist.  It  is  too  small  and  too 
low  down  to  be  the  maxillary  sinus,  therefore  we  are  led  to 
believe  that  its  existence  must  be  due  to  some  pathological 
condition.     Where  these  dark  areas  are  found  in  the  alveolar 

181 


process,  and  are  not  natural  cavities,  such  as  the  antrum  and 
the  nasal  cavities,  and  where  they  are  markedly  circumscribed, 
that  is  having  a  distinct  and  abrupt  line  of  demarkation  between 
the  dark  area  and  its  surrounding  tissue,  we  can,  in  nearly 
every  case,  make  the  positive  diagnosis  of  alveolar  abscess. 

If  the  abscess  cavity  contains  any  quantity  of  pus  the  area 
is  generally  particularly  dark.  This  is  caused  by  the  fact  that 
pus  has  been  found  to  he  fluorescent  under  the  influence  of  the 
X  Ray.  This  fluorescence  increases  the  radiations  that  affect 
the  film  in  this  particular  area,  consequently  producing  a  greater 
reaction  on  the  sensitive  emulsion,  which  shows  on  the  negative 
as  accentuated  dark  areas.  From  this  we  deduce  the  fact  that 
in  many  cases  where  the  area  is  particularly  black  the  abscess 
cavity  will  probably  contain  pus. 

In  the  case  in  question  (Figure  29)  we  note  that  the  area 
is  circumscribed  and  that  it  is  decidedly  dark  as  compared 
with  the  normal  tissue.  We  can  safely  say  that  in  this  case 
we  have  a  well-developed  alveolar  abscess  that  is  quite  active. 

The  etiology  of  this  abscess  is  also  quite  apparent  and, 
furthermore,  was  borne  out  by  the  clinical  history.  The  patient, 
a  Mr.  D.,  presented  at  the  Clinic,  with  intense  pain,  over  the 
region  of  the  bicuspid  that  had  recently  been  capped.  The 
radiograph  was  taken  and  the  diagnosis  of  alveolar  abscess  was 
at  once  made  certain.  The  cap  was  removed,  the  filling  material 
drilled  out,  and  drainage  established  through  the  apex.  The 
pain  disappeared  and  the  condition  commenced  to  improve. 
After  the  canal  had  been  open  for  some  days  and  the  active 
process  subsided,  the  canal  was  again  filled,  but  this  time  to 
the  apex,  and  the  cap  once  more  replaced. 

In  this  case  the  pulp  had  been  devitalized,  and  in  the 
removal  some  of  it  was  left  at  the  apical  end  of  the  canal. 
This  portion  of  the  dead  pulp  was  sealed  in  by  the  filling 
material  that  partly  filled  the  canal,  with  the  result  that  the 
gases  of  putrefaction  were  given  off  and  forced  through  the 
apical  foramen,  starting  up  an  inflammation  of  the  perice- 
mentum.    If  a  radiograph  had  been  taken  at  this  stage  just  a 

182 


slightly  enlarged  portion  of  the  dark  line  surrounding  the  root 
would  be  apparent  at  the  apex.  Pericementitis  may  be  deter- 
mined by  the  X  Ray,  even  before  the  patient  feels  any  real 
pain.  In  the  case  in  question  the  pericementitis  was  not  taken 
care  of,  and  the  condition  went  on  to  the  stage  of  abscess  with 
its  consequent  destruction  of  tissue,  and  the  formation  of  pus, 
before  the  patient  presented  for  treatment.  If  radiographs  were 
taken  from  time  to  time  after  an  abscess  area  has  been 
evacuated  and  drained,  the  process  of  repair  will  be  seen.  At 
first  a  distinct  whitish  line  will  be  noted  surrounding  the  area 
of  destruction.  This  line  indicating  increased  density,  probably 
represents  an  extra  deposition  of  lime  salts  over  the  walls  of 
the  abscess  cavity,  being  an  effort  of  nature  to  check  the  further 
destruction  of  cancellous  bone  tissue.  Granulation  would  then 
be  noticed  by  the  slightly  whitish  tint  inside  the  white  line 
of  demarkation.  This  would  gradually  fill  in  toward  the  center 
of  the  cavity,  and  the  shade  would  get  lighter  and  lighter  as 
the  density  of  the  tissue  increases.  As  osseous  tissue  in  time 
develops,  the  density  of  the  abscess  area  more  closely  resembles 
the  healthy  tissue  adjacent  to  it,  and,  in  fact,  ultimately  takes 
on  the  characteristic  network  appearance  of  the  normal  alveolar 
process. 

Before  leaving  Figure  29  we  will  call  attention  to  the 
absorption  of  the  alveolar  process  consequent  to  the  extraction 
of  the  second  bicuspid  and  molar  teeth. 

Case  II.,  Figure  30,  represents  another  typical  case  of 
alveolar  abscess  surrounding  the  apex  of  the  superior  left 
lateral  incisor  tooth.  In  this  case  the  pus  sac  has  ruptured 
and  the  pus  has  infiltrated  into  the  surrounding  process  as 
indicated  by  the  slightly  darker  appearance  extending  down- 
ward toward  the  roots  of  the  bicuspid  and  central  incisor  teeth. 
This  darker  appearance  is  caused  in  all  probability  by  the 
fluorescence  of  the  pus,  and  not  to  any  destruction  of  tissue. 
If  the  condition  were  allowed  to  go  on,  however,  necrosis  would 
inevitably  set  in.  The  cause  of  this  abscess  is  the  same  as  in 
Case  I.,  and  the  partial  root  filling  is  to  be  particularly  noted. 

183 


Case  III.,  Figure  31,  shows  another  abscess  on  the  distal 
root  of  the  inferior  right  second  molar.  Again,  note  the  piece 
of  filling  material  just  at  the  opening  of  the  distal  root  canal. 
The  operator  in  this  case  was  under  the  impression  that  the 
root  had  been  perfectly  filled ! 

Case  IV.,  Figure  32,  represents  another  alveolar  abscess 
involving  the  superior  left  central  and  lateral  incisor  teeth. 
In  this  case  the  repair  is  taking  place  and  the  root  canals  are 
refilled.  Note  the  appearance  of  the  filling-in  tissue,  the  only 
very  dark  area  remaining,  being  directly  around  the  root  of  the 
central.  Above  the  abscess  area  there  appears  a  white  line 
running  obliquely  downward  toward  the  median  line,  with  a 
dark  area  to  the  right  of  it,  and  one  to  the  left  of  it  higher  up. 
The  former  area  represents  the  nasal  cavity  and  the  latter  the 
anterior  part  of  the  left  maxillary  sinus.  The  white  line  is 
the  floor  of  the  nasal  cavity.  Note  the  increased  density  of  the 
maxillary  suture.  At  the  apex  of  the  right  central  we  see  a 
slightly  dark  area,  indicating  the  presence  of  an  inflammation 
of  the  periosteum.  This  is  hardly  large  enough  to  be  classed 
as  an  abscess. 

Case  v.,  Figure  33,  shows  an  active  abscess  in  the  socket 
of  the  superior  left  lateral  incisor  tooth,  which  has  been 
extracted.  A  slight  involvement  (5f  the  apex  of  the  cuspid  is 
also  seen.  Above  the  bicuspid  region  you  will  note  two  dark 
areas  surrounded  by  a  white  line.  These  areas  represent  two 
chambers  of  the  antrum  cavity,  the  white  lines  indicating  the 
exterior  walls,  the  shadows  of  which  are  thrown  downward 
and  superimposed  over  the  alveolar  process.  The  dark  area 
inside  denotes  the  normal  antrum  cavity.  The  heavier  white 
line  above  represents  the  osseous  tissue  dividing  the  posterior 
floor  of  the  nasal  cavity  and  the  hard  palate.  Note  that  the 
antrum  cavity  is  seen  to  extend  above  this  white  line,  due  to 
the  superimposition  of  the  shadows.  This  representation  of  the 
antrum  cavity  is  seen  quite  frequently  in  the  radiograph  and 
great  care  and  judgment  must  be  exercised  not  to  misinterpret  ,. 
the  normal  antrum  cavity  for  large  filling-in  abscess  areas. 

184 


Cases  VI.  and  VIL,  Figures  34  and  35,  present  two  more 
typical  radiographs  of  alveolar  abscess  where  the  destruction 
has  been  great.  In  Case  VIL  we  observe  an  involvement  of 
the  nasal  cavity  with  a  communicating  sinus. 

We  will  now  consider  some  cases  of  necrosis.  Case  VIII., 
Figure  36,  is  particularly  interesting,  since  it  shows  on  the  one 
picture  the  radiographic  difference  between  abscess  and  necrosis. 
On  examination  the  radiograph  presents  a  large  abscess  cavity 
involving  the  roots  of  the  superior  right  central  and  lateral 
incisors  and  the  cuspid  teeth.  The  upper  or  palatal  portion 
gradually  shades  off  from  dark  to  light,  while  the  lower  portion 
shows  a  distinct  line  of  demarkation.  The  upper  portion  is 
necrotic!  This  constitutes  the  difference.  Where  there  is  an 
accompanying  death  of  tissue  the  process  becomes  thoroughly 
infiltrated  with  pus,  and  a  condition  that  might  be  termed 
rarefying  ostitis  obtains.  The  gradation  of  shadow  between  the 
healthy  and  the  necrotic  bone  structure  becomes  less  and  less 
apparent.  We  may  say  that  wherever  we  observe  dark  areas 
gradually  shading  into  lighter  ones  THE  CONDITION  IS 
CHARACTERISTIC  OF  NECROSIS.  Note  also  in  Figure  36 
that  the  apex  of  the  central  root  is  absorbed. 

Cases  IX.  to  XIV.,  inclusive  (Figures  37  to  42,  inclusive), 
are  all  typical  necrosis  cases.  They  should  be  well  studied  and 
compared  with  the  series  on  alveolar  abscess  just  preceding. 
Figure  41  (Case  XIII.)  shows  a  necrotic  condition  of  the 
maxillary  suture. 

Case  XV.,  Figure  43,  presents  an  interesting  study  of 
maxillary  sinusitis.  Almost  the  entire  antrum  is  shown  in  this 
radiograph.  The  fistula  connecting  the  antrum  with  the  old 
abscess  cavity  that  is  still  active  in  the  center  is  well  shown, 
as  well  as  the  extensive  necrosis  inside  the  antrum,  and  of  the 
process. 

One  of  the  foremost  uses  of  the  radiograph  to  the  dental 
surgeon  is  its  application  to  the  study  of  root  canal  fillings. 
It  would  surprise  the  average  dentist  to  see  the  result  of  a 
hundred  radiographs  of  root  fillings  made  by  some  of  the  best 

185 


men  in  the  country.  In  many  cases,  where  the  operator  believes 
that  he  has  reached  the  apex,  a  radiographic  view  of  his  work 
would  prove  to  him  that  this  is  not  the  case.  The  author 
firmly  believes  the  time  is  coming,  and  perhaps  not  so  far 
distant,  that  every  reputable  dentist  will  ascertain  by  this  abso- 
lutely sure  method  of  investigation  the  result  of  each  root 
filling  he  makes.  Let  us  examine  a  few  cases  taken  at  random 
from  the  author's  collection.  Some  of  these  were  from  cases 
made  by  students  of  the  clinic,  while  others  were  from  estab- 
lished practitioners.  The  reader  may  judge  for  himself  which 
cases  belonged  to  the  former  and  which  to  the  latter. 

Case  XVI.,  Figure  44,  represents  the  perfect  filling  of  an 
inferior  second  bicuspid.  This  filling,  moreover,  is  a  gold  filling, 
and  extends,  as  you  will  see,  clear  down  to  the  very  apex 
of  the  root.  Unfortunately  we  do  not  meet  with  many  cases 
where  this  result  is  obtained. 

Let  us  contrast  the  last  case  with  Case  XVII. ,  Figure  45. 
Here  we  see  that  the  operator  has  succeeded  in  reaching  the 
apex  of  the  lateral  root,  and  has  even  gone  beyond.  The  result 
of  this  overzealousness  is  observed  when  we  examine  the 
rarefying  ostitis  surrounding  the  root.  Also  note  the  extent 
of  the  cuspid  filling.  In  the  first  bicuspid  we  see  a  curved 
apex  and  a  faint  white,  narrow  line  extending  nearly  to  the 
apical  foramen.  This  is  the  remains  of  a  broach  which  had 
been  left  there  during  the  extraction  of  the  pulp,  and  the  filling 
material  placed  in  the  canal  on  top  of  it. 

Case  XVIIL,  Figure  46,  represents  a  case  where  a  piece 
of  an  instrument  has  been  left  in  the  canal  of  a  superior  right 
central  incisor.  Furthermore,  in  the  effort  to  remove  this 
foreign  body  from  the  canal,  the  side  of  the  canal  has  been 
perforated  and  an  active  abscess  developed  as  seen  in  the 
picture  between  the  central  and  lateral  incisors.  The  perforation 
is  not  discernible  in  the  radiograph,  since  it  is  in  a  plane  at 
right  angles  to  the  direction  of  the  rays. 

Case  XIX.,  Figure  47,  shows  how  a  perforation  may  be 
found  by  the  radiograph.     A  wire  is  passed  up  into  the  canal 

186 


and  the  exposure  made  while  it  is  temporarily  held  in  place 
with  a  gutta-percha  seal.  The  abscess  resulting  in  this  case 
is  well  shown. 

Case  XX.,  Figure  48,  shows  where  two  wires  are  sealed 
in  the  root  canal  for  the  ascertaining /6f  a  perforation,  and  to 
see  if  the  apex  of  the  canal  has  been  reached. 

Case  XXI.,  Figure  49,  is  another  example  of  perforated 
root  canal,  with  a  large  quantity  of  filling  material  pushed 
through  into  the  process.     The  result  is  apparent. 

The  shadows  cast  by  filling  materials  vary  but  little  in 
their  relative  gradations.  Oxychloride,  gutta-percha  and 
cement  have  about  the  same  density  when  used  as  root-filling 
material.  Gold  and  amalgam  cast  slightly  whiter  shadows. 
'Mummifying  Paste'  has  about  the  same  density  as  the  tooth 
structure  itself,  consequently  a  canal  so  filled  appears  as  a 
root  without  a  canal. 

Case  XXII. ,  Figure  50,  shows  the  radiographic  appearance 
of  normal  unerupted  teeth  in  the  mouth  of  a  child.  Note  that 
in  the  unerupted  teeth  the  roots  have  not  yet  developed. 

Case  XXIIL,  Figure  51,  represents  the  impaction  of  two 
molars,  crown  to  crown,  against  each  other. 

Case  XXIV.,  Figure  52,  shows  a  central  incisor  erupting 
at  right  angles  to  its  normal  axis. 

Cases  XXV.  and  XXVI.,  Figures  53  and  54,  show  a 
superior  first  and  second  bicuspid,  respectively,  erupting  upward. 
This  is  rather  an  unusual  position  for  impacted  bicuspids. 

Case  XXVII.,  Figure  55,  is  a  very  rare  type  of  inferior 
first  molar  impaction.  Note  as  well  that  the  third  molar  which 
can  just  be  seen  at  the  extreme  left  of  the  radiograph  is  also 
impacted  against  the  second  molar. 

Cases  XXVIII.  and  XXIX.,  Figures  56  and  57,  illustrate 
another  class  of  cases  where  the  X  Ray  is  of  the  greatest  use 
to  the  dentist.  This  is  where  there  are  old  roots  left  in  the 
alveolus  after  extraction,  and  remain  there,  often  unsuspected 
by  the  patient  for  years,  till,  at  length,  through  the  absorption 
of  the  process,  their  ragged  edge  digs  into  the  gum  tissue  and 

187 


causes  great  discomfort.  Their  extraction  is  often  very  difficult 
without  the  aid  of  a  radiograph,  and  is  accompanied  by  the 
injuring  of  an  unnecessarily  large  amount  of  gum  tissue  in  the 
effort  to  locate  them  after  the  gum  has  healed  over. 

The  foregoing  twenty-nine  cases  are  but  examples  of  many 
that  might  be  cited  to  demonstrate  the  usefulness  of  the  ray 
to  the  up-to-date  dentist.  But  it  was  not  the  intention  of  the 
author  to  reproduce  these  radiographs  for  that  purpose,  but 
rather  to  serve  as  a  type  of  the  more  important  classes  of 
cases,  and  to  show  the  student  of  the  subject  how  to  go  about 
their  proper  translation,  to  the  end  that  they  may  become  used 
to  the  reading  of  these  X  Ray  shadows  and  so  make  more 
accurate  diagnoses  of  conditions.  We  might  go  on  illustrating 
cases,  ad  libitum,  where  new  and  interesting  conditions  present, 
but  the  author  prefers  in  this  volume  to  limit  these  cases  to 
the  ones  already  shown,  rather  than  to  flounder  in  an  unending 
sea  of  radiographs,  the  explanation  of  which  could  not  possibly 
be  contained  in  this  present  text  book.  At  some  future  time, 
however,  the  author  hopes  to  present  to  his  readers  another 
volume  dealing  more  specifically  with  individual  cases. 

Figure  58  represents  a  radiograph  of  the  head  taken  on  a 
glass  plate.  Note  particularly  how  well  the  inferior  dental 
canal  and  foramen  are  shown.  This  picture  was  made  by  the 
author  with  an  exposure  of  twenty  seconds,  at  a  distance  from 
anode  to  plate  of  twenty-eight  inches  (the  maximum  distance 
that  would  be  used),  while  testing  the  new  standard  dental  outfit 
manufactured  by  the  American  X  Ray  Equipment  Co.  of 
New  York. 


188 


NOTES 


189 


NOTES 


190 


CHAPTER  XIX. 
Stereoscopic  Radiographs  of  the  Teeth 

Stereoscopic  radiographs  of  the  teeth  and  adjacent  tissues 
were  first  made  and  shown  by  the  author  in  1905.  Since  that 
date  Httle  has  been  done  with  them  owing  to  the  difficult 
technique  involved. 

There  are  many  cases  where  it  is  very  desirable  to  separate 
the  superimposed  planes  of  the  ordinary  radiograph.  For 
example,  suppose  we  have  a  picture  showing  two  roots  directly 
superimposed  on  each  other,  a  very  frequent  occurrence,  and 
let  us  further  suppose  that  an  abscess  area  is  shown  pointing 
upward  from  the  apices  of  the  roots.  The  natural  question 
that  arises  is,  from  which  root  does  the  abscess  originate?  It  is 
impossible  to  positively  determine  this  from  the  flat  single  pic- 
ture, but  if  we  make  stereoscopic  radiographs  of  the  condition 
and  view  them  through  a  stereoscope  the  teeth  stand  out  and 
take  on  the  rotundity  that  they  would  have  if  actually  viewed 
by  the  eyes  in  the  dissected  jaw.  In  other  words,  we  would 
appreciate  the  several  planes  separately,  and  objects  would 
appear  to  have  all  three  dimensions.  The  original  stereoscopic 
radiographs  made  by  the  author  eight  years  ago  were  printed 
positives  and  viewed  with  the  ordinary  photographic  stereo- 
scope. The  difficulty  in  the  technique  of  making  these  pictures 
was  twofold.  First  it  was  essential  to  take  two  radiographs 
of  the  teeth  to  be  examined,  from  two  viewpoints  separated  the 
normal  distance  that  we  have  between  the  pupils  of  the  eyes. 
To  do  this  we  had  to  move  the  X  Ray  tube  just  two  and  a 
half  inches  (the  average  pupilary  distance)  in  a  lateral  plane 
between  the  exposures,  at  the  same  time  preserving  the  same 
relative  position  with  regard  to  all  other  planes.  Secondly,  we 
had  to  remove  the  first  film  from  the  mouth  and  substitute  the 
second   for   the   dual   exposure,   the   second   film   having  to   be 

191 


placed  in  exactly  the  same  position  with  regard  to  the  tissues 
as  the  first. 

The  author  has  recently  perfected  a  comparatively  simple 
technique  for  the  ov?erconiing  of  these  heretofore  difficult  fea- 
tures. A  small  plumb-bob  is  suspended  from  one  of  the 
terminals  of  the  tube  shield  and  this  is  allowed  to  hang  freely 
directly  over  a  yardstick  that  is  mounted  in  a  horizontal  plane 
coinciding  with  the  plane  in  which  the  tube  must  be  moved 
during  the  exposure.  The  first  picture  is  taken,  and  the  tube 
shield  moved  along  till  the  plumb-bob  has  traversed  just  two 
and  a  half  inches  on  the  yardstick  and  the  second  exposure 
made.  To  insure  the  placing  of  the  second  film  in  the  abso- 
lutely same  position  as  the  first,  an  impression  of  the  part  of  the 
superior  arch  that  we  wish  to  radiograph  is  first  made  with 
wax  on  a  'bite-plate,'  and  while  the  wax  is  still  soft  the  film 
packet  is  pressed  into  the  impression  in  the  proper  position 
until  it  leaves  an  indentation.  The  film  packet  is  then  removed, 
the  wax  chilled,  and  the  film  packet  replaced.  The  whole  im- 
pression with  the  film  is  then  replaced  in  the  mouth,  the  patient 
getting  the  same  bite  and  the  first  exposure  made.  The  second 
exposure  is  made  in  the  same  way,  the  second  film  packet  being 
placed  in  the  same  indentation  in  the  wax.  This  same  pro- 
cedure can  be  carried  out  with  the  lower  arch  by  the  use  of  a 
partial  impression  tray  with  the  outer  w^all  cut  away.  These 
bite  plated  and  impression  trays  may  be  obtained  from  the 
S.  S.  White  Co.  of  Philadelphia. 

This  method  of  holding  the  film  in  the  mouth  may  be 
used  as  well  for  ordinary  radiographs  in  cases  where  there  is 
difficulty  in  the  patient  holding  it. 

The  author  has  also  recently  improved  the  old  method  of 
viewing  the  stereoscopic  radiographs.  Formerly  it  was  neces- 
sary to  print  and  mount  the  stereoscopic  pictures  before  they 
could  be  placed  in  the  stereoscope,  but  now  the  negatives  are 
used  themselves.  They  are  placed  in  an  instrument  that  the 
author  has  termed  a  dental  'Radioscope.'  This  is  illustrated 
in  Figures  59  and  60. 

192 


Figure  59  represents  an  actual  photographic  view  of  the 
instrument,  while  Figure  60  shows  the  interior  construction 
being  a  top  view  with  the  cover  removed.  A  light  tight 
viewing  box  is  constructed  with  two  mirrors,  C  and  D,  mounted 
at  right  angles  to  each  other.  The  two  stereoscopic  films  are 
mounted  in  the  regular  dental  celluloid  mounts  and  are 
respectively  inserted  in  slots  and  grooves  at  either  side  of  the 
mirrors,  as  A  and  B.  The  films,  when  so  inserted,  coming 
directly  in  front  of  two  windows,  F  and  G.  The  film  on  the 
right  is  capable  of  fine  adjustment  by  the  set  screw  K  for 
lateral  movement,  and  another  set  screw  on  the  cover  of  the 
box  (shown  in  Figure  59),  which  presses  against  the  spring  L 
for  vertical  adjustment.  The  lamps,  H,  at  either  end  of  the 
box  are  lighted,  and  the  observer  looks  through  the  hood  E. 
The  right  eye  sees  the  reflection  of  the  right  negative  in  the 
mirror,  D,  through  the  lens,  Y,  while  the  left  eye  sees  the 
other  negative  in  the  mirror,  C,  through  the  lens,  X.  The 
negatives  are  equally  illuminated  by  the  lamps,  and  if  we 
manipulate  the  fine  adjustment  screw^s  till  the  images  of  the 
two  radiographs  register  perfectly,  we  will  perceive  a  perfect 
stereoscopic  aspect  of  the  combined  negatives.  The  hood,  E, 
can  be  moved  in  or  out  till  the  focus  of  the  lenses  are  adjusted 
to  suit  the  eyes  of  the  observer. 

Radiographs  taken  and  viewed  in  this  manner  show  far 
more  detail  than  the  ordinary  negatives,  and  in  obscure  cases 
should  always  be  resorted  to  if  the  operator  wishes  to  give  his 
patient  the  benefit  of  the  best  means  of  diagnosis  obtainable. 
In  developing  these  pictures  care  should  be  taken  to  develop 
them  an  equal  length  of  time  so  that  they  will  have  the  same 
relative  density.  The  same  is  true  for  the  original  exposure. 
While  this  book  is  going  to  press,  the  author  is  working 
on  a  new  method  by  which  he  has  succeeded  in  doing  away 
with  the  double  exposure  altogether.  When  this  method,  which 
the  author  has  termed  ''the  radioscopic  method  of  examination," 
is  perfected  it  should  so  simplify  the  making  of  these  pictures 
that  they  may  be  employed  in  every  routine  case. 

193 


NOTES 


194 


CHAPTER  XX. 
Conclusion 

In  the  preceding  chapters  the  author  has  tried  to  bring 
before  his  readers  the  entire  subject  of  Dental  Radiology  in 
as  clear  and  at  the  same  time  comprehensive  a  manner  as 
possible  through  the  medium  of  text  and  illustrations.  There 
are  many  points,  however,  that  are  hard  to  explain  by  these 
means.  Particularly  is  this  true  in  regard  to  the  coloration  of 
the  X  Ray  tubes.  It  will  be  only  with  experience  that  the 
operator  can  gain  the  ultimate  success  for  which  he  is  working. 
At  the  same  time  the  cloak  of  mystery  that  has  for  so  long 
enshrouded  the  X  Ray  and  all  pertaining  to  it  has  been  steadily 
shrinking,  till  we  can  at  last  say  that  it  is  a  working  science. 
The  author  has  endeavored  to  give,  throughout  the  book,  the 
benefit  of  all  'short  cuts'  and  discoveries  that  he  has  worked 
out  in  a  practice  of  over  twelve  years,  particularly  devoted  to 
the  study  of  the  dental  aspect  of  Radiology. 

Students  of  this  subject  should  pay  particular  attention 
to  the  precautions  that  should  be  taken  to  make  its  practice 
both  safe  and  harmless.  It  is  a  wonderful  agent  that  has  been 
placed  at  our  disposal,  but  it  should  not  be  abused.  It  has  its 
limitations  like  every  other  branch  of  science,  but  properly 
and  safely  used  it  can  do  a  great  deal  of  good  to  suffering 
humanity. 

Before  closing  it  would  seem  desirable  to  give  to  the 
student  starting  out  in  the  practice  of  Dental  Radiology  a  few 
hints  and  suggestions  as  to  zvhat  not  to  do. 

DON'T  EXPOSE  YOURSELF  UNDER  ANY  CONSIDERA- 
TION TO  THE  X  RAYS. 

DON'T  ALLOW  YOUR  PATIENT  TO  SIT  IN  THE  PATH 
OF  THE  RAYS  WHILE  YOU  ARE  TESTING  TUBES. 

195 


DON'T  KEEP  YOUR  PATIENT  IN  AN  UNCOMFORT- 
ABLE POSITION  WHILE  YOU  ARE  ADJUSTING 
YOUR  TUBE. 

DON'T  BE  TOO  SURE  OF  THE  RESULT  OF  THE 
PICTURE. 

DON'T  MAKE  TOO  BIG  CLAIMS  FOR  YOUR  KNOWL- 
EDGE OF  RADIOGRAPHIC  DIAGNOSIS. 

DON'T  HOLD  FILMS  IN  THE  MOUTH  YOURSELF. 

DON'T  TRY  TO  COVER  TOO  LARGE  AN  AREA  WITH 
ONE  FILM. 

DON'T  USE  PLATES  IF  YOU  CAN  GET  THE  AREA 
ON  A  FILM  IN  THE  MOUTH. 

DON'T  USE  OLD  FILMS  OR  DEVELOPER. 

DON'T  LEAVE  YOUR  FILMS  WRAPPED  TOO  LONG 
IN  RUBBER. 

DON'T  FAIL  TO  PRESERVE  A  COPY  OF  YOUR 
NEGATIVE. 

DON'T  FAIL  TO  NUMBER  AND  FILE  ALL  THESE 
COPIES. 

DON'T  ABUSE  YOUR  TUBE;  LET  IT  REST  OCCASION- 
ALLY FOR  A  WEEK  AT  A  TIME. 

DON'T  ATTEMPT  TO  TAKE  PICTURES  OF  OTHER 
PARTS  OF  THE  BODY  FOR  PATIENTS  UNLESS 
YOU  HAVE  HAD  INSTRUCTION. 

DON'T  TRY  TO  DRY  YOUR  NEGATIVES  BY  HEAT 
OR  IN  THE  SUN. 

196 


DON'T  TAKE  A  RADIOGRAPH  OF  A  PATIENT  UN- 
LESS THERE  IS  A  WITNESS  IN  THE  ROOM. 

DON'T  TAKE  RADIOGRAPHS  OF  PATIENTS  FOR 
RIDICULOUSLY  LOW  FEES.  BETTER  TAKE  IT 
FOR  NOTHING  THAN  TO  UNDERESTIMATE  YOUR 
SERVICES. 

DON'T  CHARGE  PROHIBITIVE  FEES,  EITHER. 

DON'T  FAIL  TO  THOROUGHLY  UNDERSTAND  THE 
WORKING  OF  YOUR  APPARATUS. 

DON'T  STORE  YOUR  FILMS  AND  PLATES  WHERE 
THEY  MAY  POSSIBLY  RECEIVE  X  RAY  EXPOSURE. 

DON'T  FAIL  TO  SWAB  OFF  YOUR  NEGATIVES  AFTER 
WASHING  WITH  ABSORBENT  COTTON. 

DON'T  ALLOW  ANYONE  TO  GET  NEAR  THE  CON- 
DUCTING WIRES  WHILE  THE  APPARATUS  IS 
WORKING. 

DON'T  HANDLE  A  WET  NEGATIVE  ANY  MORE 
THAN  NECESSARY. 

DON'T  FAIL  TO.  TAKE  A  RADIOGRAPH  IN  EVERY 
CASE  WHERE  YOU  THINK  IT  WILL  BE  OF  BENE- 
FIT TO  YOU  OR  YOUR  PATIENT. 


the;  e:nd. 


197 


NOTES 


198 


NOTES 


199 


STAMPED  BELOW 

.rmTAT   VINE  OF  25  CENTS 
AN  INITIAL  Fl"%  "' „E  TO  BcruRN 

^,^^  3E  ^^^n^r/oTxE  DUE    THE  PENALTY 
THIS  BOOK  °N   T  „%o  cIn?s  ON  THE  FOURTH 

OAY     AND    TO     9^-^^ 
OVERDUE. 


LD  2l-5rri-7,'J 


M 


RSITY  OF  CALIFORNIA  LIBRARY 


